We present an analysis of the stellar mass growth over the last 10 Gyr ($z\le 2$) using a unique large sample of galaxies selected at $3.6~\mu$m. We have assembled accurate photometric and ...spectroscopic redshifts for ~21 200 and 1500 galaxies, respectively, with F(3.6 μm) ≥ 9.0 μJy by combining data from Spitzer-SWIRE IRAC, the VIMOS VLT Deep Survey (VVDS), UKIDSS and very deep optical CFHTLS photometry. We split our sample into quiescent (red) and active (blue) galaxies on the basis of an SED fitting procedure that we have compared with the strong rest-frame color bimodality $(NUV-r')_{\rm ABS}$. The present sample contains ~ 4400 quiescent galaxies. Our measurements of the K-rest frame luminosity function and luminosity density evolution support the idea that a large fraction of galaxies is already assembled at z ~ 1.2, with almost 80% and 50% of the active and quiescent populations already in place, respectively. Based on the analysis of the evolution of the stellar mass-to-light ratio (in K-band) for the spectroscopic sub-sample, we derive the stellar mass density for the entire sample. We find that the global evolution of the stellar mass density is well reproduced by the star formation rate derived from UV based measurements when an appropriate dust correction is applied, which supports the idea of an initial mass function that is on average universal. Over the last 8 Gyr (z ≤ 1.2) we observe that the stellar mass density of the active population shows a modest mass growth rate ($\dot{\rho}$ ~ 0.005(±0.005) $M_{\odot}$/Mpc3/yr), consistent with a constant stellar mass density, $\rho_{\star}^{\rm active}$ ~ 3.1 $\times$ 108 $M_{\odot}$/Mpc3. In contrast, an increase by a factor of ~2 for the quiescent population over the same timescale is observed. As a consequence, the growth of the stellar mass in the quiescent population must be due to the shutoff of star formation in active galaxies that migrate into the quiescent population. We estimate this stellar mass flux to be $\dot{\rho}_{A\rightarrow Q}$ ~ 0.017(±0.004) $M_{\odot}$/Mpc3/yr, which balances the major fraction of new stars born according to our best SFR estimate ($\dot{\rho}$ = 0.025(±0.003) $M_{\odot}$/Mpc3/yr). From $z = 2$ to $z = 1.2$, we observe a major build-up of the quiescent population with an increase by a factor of ~10 in stellar mass (a mass growth rate of ~ 0.063 $M_{\odot}$/Mpc3/yr). This rapid evolution suggests that we are observing the epoch when, for the first time in the history of the universe, an increasing fraction of galaxies end their star formation activity and start to build up the red sequence.
Aims. We present and release photometric redshifts for a uniquely large and deep sample of 522286 objects with $i'_{\rm AB}\le 25$ in the Canada-France Hawaii Telescope Legacy Survey (CFHTLS) “Deep ...Survey” fields D1, D2, D3, and D4, which cover a total effective area of 3.2 $\deg^2$. Methods. We use 3241 spectroscopic redshifts with $0 \leq z \leq 5$ from the VIMOS VLT Deep Survey (VVDS) as a calibration and training set to derive these photometric redshifts. Using the “Le Phare” photometric redshift code, we developed a robust calibration method based on an iterative zero-point refinement combined with a template optimisation procedure and the application of a Bayesian approach. This method removes systematic trends in the photometric redshifts and significantly reduces the fraction of catastrophic errors (by a factor of 2), a significant improvement over traditional methods. We use our unique spectroscopic sample to present a detailed assessment of the robustness of the photometric redshift sample. Results. For a sample selected at $i'_{\rm AB}\le 24$, we reach a redshift accuracy of $\sigma_{\Delta z/(1+z)}=0.029$ with $\eta=3.8\%$ of catastrophic errors (η is defined strictly as those objects with $|\Delta z|/(1+z) > 0.15$). The reliability of our photometric redshifts decreases for faint objects: we find $\sigma_{\Delta z/(1+z)}=0.025, 0.034$ and $\eta=1.9\%, 5.5\%$ for samples selected at $i'_{\rm AB}=17.5$–22.5 and 22.5–24 respectively. We find that the photometric redshifts of starburst galaxies are less reliable: although these galaxies represent only 22% of the spectroscopic sample, they are responsible for 50% of the catastrophic errors. An analysis as a function of redshift demonstrates that our photometric redshifts work best in the redshift range $0.2\le z \le 1.5$. We find an excellent agreement between the photometric and the VVDS spectroscopic redshift distributions at $i'_{\rm AB}\le 24$. Finally, we compare the redshift distributions of i' selected galaxies on the four CFHTLS deep fields, showing that cosmic variance is still present on fields of 0.7–0.9 deg2. These photometric redshifts are made publicly available at http://terapix.iap.fr (complete ascii catalogues) and http://cencos.oamp.fr/cencos/CFHTLS/ (searchable database interface).
Observations of distant supernovae indicate that the Universe is now in a phase of accelerated expansion the physical cause of which is a mystery. Formally, this requires the inclusion of a term ...acting as a negative pressure in the equations of cosmic expansion, accounting for about 75 per cent of the total energy density in the Universe. The simplest option for this 'dark energy' corresponds to a 'cosmological constant', perhaps related to the quantum vacuum energy. Physically viable alternatives invoke either the presence of a scalar field with an evolving equation of state, or extensions of general relativity involving higher-order curvature terms or extra dimensions. Although they produce similar expansion rates, different models predict measurable differences in the growth rate of large-scale structure with cosmic time. A fingerprint of this growth is provided by coherent galaxy motions, which introduce a radial anisotropy in the clustering pattern reconstructed by galaxy redshift surveys. Here we report a measurement of this effect at a redshift of 0.8. Using a new survey of more than 10,000 faint galaxies, we measure the anisotropy parameter = 0.70 ± 0.26, which corresponds to a growth rate of structure at that time of f = 0.91 ± 0.36. This is consistent with the standard cosmological-constant model with low matter density and flat geometry, although the error bars are still too large to distinguish among alternative origins for the accelerated expansion. The correct origin could be determined with a further factor-of-ten increase in the sampled volume at similar redshift.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We present a detailed analysis of the Galaxy Stellar Mass Function (GSMF) of galaxies up to z =2.5 as obtained from the VIMOS VLT Deep Survey (VVDS). Our survey offers the possibility to investigate ...the GSMF using two different samples: (1) an optical ( I-selected 17.5 <I_{\rm AB}<24) main spectroscopic sample of about 6500 galaxies over 1750 arcmin super(2) and (2) a near-IR ( K-selected K_{\rm AB}<22.34 similar to {\rm and} similar to K_{\rm AB}<22.84) sample of about 10 200 galaxies, with photometric redshifts accurately calibrated on the VVDS spectroscopic sample, over 610 arcmin super(2). We apply and compare two different methods to estimate the stellar mass {\cal M}_{\rm stars} from broad-band photometry based on different assumptions about the galaxy star-formation history. We find that the accuracy of the photometric stellar mass is satisfactory overall, and show that the addition of secondary bursts to a continuous star formation history produces systematically higher (up to 40%) stellar masses. We derive the cosmic evolution of the GSMF, the galaxy number density and the stellar mass density in different mass ranges. At low redshift ( z\simeq0.2) we find a substantial population of low-mass galaxies (<10 { similar to M_\odot) composed of faint blue galaxies ( M_I-M_K \simeq 0.3). In general the stellar mass function evolves slowly up to z\sim0.9 and more rapidly above this redshift, in particular for low mass systems. Conversely, a massive population is present up to z =2.5 and has extremely red colours ( M_I-M_K\simeq 0.7-0.8). We find a decline with redshift of the overall number density of galaxies for all masses (59\pm5% for 10 proportional to similar to M_\odot$--> {\cal M}_{\rm stars} > 10 proportional to similar to M_\odot at z =1), and a mild mass-dependent average evolution ("mass-downsizing"). In particular our data are consistent with mild/negligible (<30%) evolution up to z\sim0.7 for massive galaxies ( }6\times10 6M_\odot$--> {>}6\times10 6M_\odot). For less massive systems the no-evolution scenario is excluded. Specifically, a large fraction ({\ge}50\%) of massive galaxies have been assembled and converted most of their gas into stars at z\sim1, ruling out "dry mergers" as the major mechanism of their assembly history below z\simeq1. This fraction decreases to {\sim}33\% at z\sim2. Low-mass systems have decreased continuously in number density (by a factor of up to 4.1\pm0.9) from the present age to z =2, consistent with a prolonged mass assembly also at z <1. The evolution of the stellar mass density is relatively slow with redshift, with a decrease of a factor of 2.3\pm0.1 at z =1 and about 4.5\pm0.3 at z =2.5.
The VIMOS VLT Deep Survey (VVDS), designed to measure 150,000 galaxy redshifts, requires a dedicated data reduction and analysis pipeline to process in a timely fashion the large amount of ...spectroscopic data being produced. This requirement has lead to the development of the VIMOS Interactive Pipeline and Graphical Interface (VIPGI), a new software package designed to simplify to a very high degree the task of reducing astronomical data obtained with VIMOS (Visible Multi–Object Spectrograph), the imaging spectrograph built by the VIRMOS Consortium for the European Southern Observatory and mounted on Unit 3 (Melipal) of the VLT (Very Large Telescope) at Paranal Observatory (Chile). VIPGI provides the astronomer with specially designed VIMOS data‐reduction functions, a VIMOS‐centric data organizer, and dedicated data browsing and plotting tools, which can be used to verify the quality and accuracy of the various stages of the data‐reduction process. The quality and accuracy of the data‐reduction pipeline are comparable to those obtained using well‐known IRAF tasks, but the speed of the data‐reduction process is significantly increased, because of the dedicated nature of VIPGI. In this paper we discuss the details of the multiobject spectroscopy (MOS) data‐reduction pipeline that has been implemented in VIPGI, as applied to the reduction of some 20,000 VVDS spectra, quantitatively assessing the accuracy of the various reduction steps. We also provide a more general overview of VIPGI capabilities, a tool that can be used for the reduction of any kind of VIMOS data.
Aims.We report on a search for faint (R total magnitude fainter than 21) and low surface brightness galaxies (R central surface brightness fainter than ~24) (fLSBs) in a $0.72 \times 0.82$ deg2 area ...centered on the Coma cluster. Methods.We analyzed deep B and R band CCD imaging obtained using the CFH12K camera at CFHT and found 735 fLSBs. The total B magnitudes, at the Coma cluster redshift, range from -13 to -9 with B central surface brightness as faint as 27 mag arcsec-2. Results.Using empty field comparisons, we show that most of these fLSBs are probably inside the Coma cluster. We present the results of comparing the projected fLSB distributions with the distributions of normal galaxies and with known X-ray over densities. We also investigate their projected distribution relative to their location in the color magnitude relation. Colors of fLSBs vary between $B-R\sim 0.8$ and ~1.4 for 2/3 of the sample and this part is consistent with the known CMR red-sequence for bright ($R\leq 18$) ellipticals in Coma. Conclusions.These fLSBs are likely to have followed the same evolution as giant ellipticals, which is consistent with a simple feedback/collapse formation and a passive evolution. These fLSBs are mainly clustered around NGC 4889. We found two other distinct fLSB populations. These populations have respectively redder and bluer colors compared to the giant elliptical red-sequence and possibly formed from stripped faint ellipticals and material stripped from spiral in-falling galaxies.
EHT0202 (etazolate hydrochloride) is a new compound exhibiting both potential disease-modifying and symptomatic treatment properties in Alzheimer's Disease increasing alpha-secretase activity and ...sAPP alpha secretion, as well as acting as a GABA-A receptor modulator and as a PDE-4 inhibitor.
This pilot, randomized, double-blind, placebo-controlled, parallel group, multicentre, Phase IIA study was conducted in 159 randomized patients suffering from mild to moderate Alzheimer's Disease. EHT0202 (40 or 80 mg bid) or placebo was administered as adjunctive therapy to one acetylcholinesterase inhibitor over a 3-month period. This study was designed to assess the clinical safety and tolerability of EHT0202 as a primary objective, with secondary endpoints (cognitive function, daily living activities, behaviour, caregiver burden and global functioning) included to explore clinical efficacy of EHT0202 versus placebo.
EHT0202 was shown to be safe and generally well tolerated. Dose-dependent numbers of early withdrawal and central nervous system related adverse events were observed. As expected, since the study was not powered and not designed to show drug efficacy, and except for ratings on the ADCS-ADL scale, no significant differences were seen between treatment groups.
These first encouraging safety results do support further development of EHT0202 in order to assess its clinical efficacy and to confirm its tolerability in a larger cohort of Alzheimer patients and for a longer period.
From first epoch observations of the VIMOS VLT Deep Survey (VVDS) we have derived luminosity functions for galaxy samples selected by spectral type out to z =1.5. With the VVDS we are able to ...investigate within the same sample the evolution of the type dependent luminosity function selected in several rest-frame bands over 70% of the age of the Universe. The simple lesssim0.5 mag for early type galaxies to similar to 1 mag for the latest type galaxies, while the slope of the luminosity function of each spectral type is consistent with being redshift-independent. The luminosity function of early type galaxies is consistent with passive evolution up to alpha, and continuum images of the Sculptor Group spiral galaxy NGC 55 obtained with the WFI instrument at the 2.2-m telescope of ESO. We identified 21 new planetary nebula candidates. We constructed the O IIIlambda5007 Planetary Nebula Luminosity Function (PNLF) and determined a most likely distance of 2.30 pm 0.35 Mpc. The distance to NGC 55 is a bit larger than previously determined distances, which means that the Sculptor Group is further away from the Local Group than previously thought. The PNLF distance to NGC 55 is comparable to the PNLF distance of NGC 300 (Soffner et al. 1996, A&A, 306, 9), adding support to the suggestion that these galaxies form a bound pair. There doesn't seem to be a shortage of planetary nebula candidates in this metal poor galaxy.
Aims.We have computed the evolution of the rest-frame B-band luminosity function (LF) for bulge and disk-dominated galaxies since z=1.2. Methods: .We use a sample of 605 spectroscopic redshifts with ...IAB? 24 in the Chandra Deep Field South from the VIMOS-VLT Deep Survey, 3555 galaxies with photometric redshifts from the COMBO-17 multi-color data, coupled with multi-color HST/ACS images from the Great Observatories Origin Deep Survey. We split the sample in bulge- and disk-dominated populations on the basis of asymmetry and concentration parameters measured in the rest-frame B-band. Results: .We find that at z=0.4-0.8, the LF slope is significantly steeper for the disk-dominated population (?=-1.19 ± 0.07) compared to the bulge-dominated population (?=-0.53 ± 0.13). The LF of the bulge-dominated population is composed of two distinct populations separated in rest-frame color: 68% of red (B-I)AB>0.9 and bright galaxies showing a strongly decreasing LF slope ?=+0.55 ± 0.21, and 32% of blue (B-I)AB<0.9 and more compact galaxies which populate the LF faint-end. We observe that red bulge-dominated galaxies are already well in place at z?1, but the volume density of this population is increasing by a factor 2.7 between z? 1 and z? 0.6. It may be related to the building-up of massive elliptical galaxies in the hierarchical scenario. In addition, we observe that the blue bulge-dominated population is dimming by 0.7 mag between z? 1 and z? 0.6. Galaxies in this faint and more compact population could possibly be the progenitors of the local dwarf spheroidal galaxies.
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