Context. High-precision, space-based photometric missions like CoRoT and Kepler have revealed new and surprising phenomena in classical variable stars. Such discoveries were the period doubling in RR ...Lyrae stars and the frequent occurrence of additional periodicities some of which can be explained by radial overtone modes, but others are discordant with the radial eigenfrequency spectrum. Aims. We search for signs of period doubling in CoRoT RR Lyrae stars. The occurrence of this dynamical effect in modulated RR Lyrae stars might help us to gain more information about the mysterious Blazhko effect. The temporal variability of the additional frequencies in representatives of all subtypes of RR Lyrae stars is also investigated. Methods. We preprocess CoRoT light curves by applying trend and jump correction and outlier removal. Standard Fourier technique is used to analyze the frequency content of our targets and follow the time-dependent phenomena. Results. The most comprehensive collection of CoRoT RR Lyrae stars, including new discoveries is presented and analyzed. We found alternating maxima and in some cases half-integer frequencies in four CoRoT Blazhko RR Lyrae stars, as clear signs of the presence of period doubling. This reinforces that period doubling is an important ingredient for understanding the Blazhko effect – a premise we derived previously from the Kepler RR Lyrae sample. As expected, period doubling is detectable only for short time intervals in most modulated RRab stars. Our results show that the temporal variability of the additional frequencies in all RR Lyrae subtypes is ubiquitous. The ephemeral nature and the highly variable amplitude of these variations suggest a complex underlying dynamics of and an intricate interplay between radial and possibly nonradial modes in RR Lyrae stars. The omnipresence of additional modes in all types of RR Lyrae – except in non-modulated RRab stars – implies that asteroseismology of these objects should be feasible in the near future.
Aims. The role of galaxy mergers in massive galaxy evolution, and in particular to mass assembly and size growth, remains an open question. In this paper we measure the merger fraction and rate, both ...minor and major, of massive early-type galaxies (M ⋆ ≥ 1011 M⊙) in the COSMOS field, and study their role in mass and size evolution. Methods. We used the 30-band photometric catalogue in COSMOS, complemented with the spectroscopy of the zCOSMOS survey, to define close pairs with a separation on the sky plane 10 h-1 kpc ≤ rp ≤ 30 h-1 kpc and a relative velocity Δv ≤ 500 km s-1 in redshift space. We measured both major (stellar mass ratio μ ≡ M ⋆ ,2/M ⋆ ,1 ≥ 1/4) and minor (1/10 ≤ μ < 1/4) merger fractions of massive galaxies, and studied their dependence on redshift and on morphology (early types vs. late types). Results. The merger fraction and rate of massive galaxies evolves as a power-law (1 + z)n, with major mergers increasing with redshift, nMM = 1.4, and minor mergers showing little evolution, nmm ~ 0. When split by their morphology, the minor merger fraction for early-type galaxies (ETGs) is higher by a factor of three than that for late-type galaxies (LTGs), and both are nearly constant with redshift. The fraction of major mergers for massive LTGs evolves faster (nMMLT ~ 4 ) than for ETGs (nMMET= 1.8). Conclusions. Our results show that massive ETGs have undergone 0.89 mergers (0.43 major and 0.46 minor) since z ~ 1, leading to a mass growth of ~30%. We find that μ ≥ 1/10 mergers can explain ~55% of the observed size evolution of these galaxies since z ~ 1. Another ~20% is due to the progenitor bias (younger galaxies are more extended) and we estimate that very minor mergers (μ < 1/10) could contribute with an extra ~20%. The remaining ~5% should come from other processes (e.g., adiabatic expansion or observational effects). This picture also reproduces the mass growth and the velocity dispersion evolution of these galaxies. We conclude from these results, and after exploring all the possible uncertainties in our picture, that merging is the main contributor to the size evolution of massive ETGs at z ≲ 1, accounting for ~50−75% of that evolution in the last 8 Gyr. Nearly half of the evolution due to mergers is related to minor (μ < 1/4) events.
We characterize near‐surface ocean diurnal warm‐layer events, using satellite observations and fields from numerical weather forecasting. The study covers April to September, 2006, over the area 11°W ...to 17°E and 35°N to 57°N, with 0.1° cells. We use hourly satellite SSTs from which peak amplitudes of diurnal cycles in SST (dSSTs) can be estimated with error ∼0.3 K. The diurnal excursions of SST observed are spatially and temporally coherent. The largest dSSTs exceed 6 K, affect 0.01% of the surface, and are seen in the Mediterranean, North and Irish Seas. There is an anti‐correlation between the magnitude and the horizontal length scale of dSST events. Events wherein dSST exceeds 4 K have length scales of ≤40 km. From the frequency distribution of different measures of wind‐speed minima, we infer that extreme dSST maxima arise where conditions of low wind speed are sustained from early morning to mid afternoon.
Context. Active galactic nuclei (AGN) are thought to play an important role in galaxy evolution. It has been suggested that AGN feedback could be partly responsible for quenching star-formation in ...the hosts, leading to transition from the blue cloud to the red sequence. The transition seems to occur faster for the most massive galaxies, where traces of AGN activity have been found as early as at z < 0.1. The correlation betweenAGN activity, aging of the stellar populations, and stellar mass still needs to be fully understood, especially at high redshifts. Aims. Our aim is to investigate the link between AGN activity, star-formation, and stellar mass of the host galaxy at 0 < z < 1, looking for spectroscopic traces of AGN and aging of the host. This work provides an extension of the existing studies at z < 0.1 and contributes to shed light on galaxy evolution at intermediate redshifts. Methods. We used the zCOSMOS 20k data to create a sample of galaxies at z < 1. We divided the sample into several mass-redshift bins to obtain stacked galaxy spectra with an improved signal-to-noise ratio (S/N). We exploited emission-line diagnostic diagrams to separate AGN from star-forming galaxies. Results. We found an indication of a role for the total galaxy stellar mass in leading galaxy classification. Stacked spectra show AGN signatures above the log M∗/M⊙ > 10.2 threshold. Moreover, the stellar populations of AGN hosts are found to be older than star-forming and composite galaxies. This could be due to the the tendency of AGN to reside in massive hosts. Conclusions. The dependence of the AGN classification on the stellar mass agrees with what has been found in previous research. Together with the evidence of older stellar populations inhabiting the AGN-like galaxies, it is consistent with the downsizing scenario. In particular, our evidence points to an evolutionary scenario where the AGN-feedback is capable of quenching the star formation in the most massive galaxies. Therefore, the AGN-feedback is the best candidate for initiating the passive evolutionary phase of galaxies.
Context.The theory of stellar evolution can be more closely tested if we have the opportunity to measure new quantities. Nowadays, observations of galactic RR Lyr stars are available on a time ...baseline exceeding 100 years. Therefore, we can exploit the possibility of investigating period changes, continuing the pioneering work started by V. P. Tsesevich in 1969. Aims.We collected the available times of maximum brightness of the galactic RR Lyr stars in the GEOS RR Lyr database. Moreover, we also started new observational projects, including surveys with automated telescopes, to characterise the O–C diagrams better. Methods.The database we built has proved to be a very powerful tool for tracing the period variations through the ages. We analyzed 123 stars showing a clear O–C pattern (constant, parabolic or erratic) by means of different least–squares methods. Results.Clear evidence of period increases or decreases at constant rates has been found, suggesting evolutionary effects. The median values are β = +0.14 d Myr-1 for the 27 stars showing a period increase and β = -0.20 d Myr-1 for the 21 stars showing a period decrease. The large number of RR Lyr stars showing a period decrease (i.e., blueward evolution) is a new and intriguing result. There is an excess of RR Lyr stars showing large, positive β values. Moreover, the observed β values are slightly larger than those predicted by theoretical models.
The aim of this paper is to introduce the WIRCam Ultra Deep Survey (WUDS), a near-IR photometric survey carried out at the CFH Telescope in the field of the CFHTLS-D3 field (Groth Strip). WUDS ...includes four near-IR bands (Y, J, H and Ks) over a field of view of ∼400 arcmin2. The typical depth of WUDS data reaches between ∼26.8 in Y and J, and ∼26 in H and Ks (AB, 3σ in 1.3″ aperture), whereas the corresponding depth of the CFHTLS-D3 images in this region ranges between 28.6 and 29 in ugr, 28.2 in i and 27.1 in z (same S/N and aperture). The area and depth of this survey were specifically tailored to set strong constraints on the cosmic star formation rate and the luminosity function brighter or around L⋆ in the z ∼ 6 − 10 redshift domain, although these data are also useful for a variety of extragalactic projects. This first paper is intended to present the properties of the public WUDS survey in details: catalog building, completeness and depth, number counts, photometric redshifts, and global properties of the galaxy population. We have also concentrated on the selection and characterization of galaxy samples at z ∼ 4.5 − 7 in this field. For these purposes, we include an adjacent shallower area of ∼1260 arcmin2 in this region, extracted from the WIRCam Deep Survey (WIRDS), and observed in J, H and Ks bands. UV luminosity functions were derived at z ∼ 5 and z ∼ 6 taking advantage from the fact that WUDS covers a particularly interesting regime at intermediate luminosities, which allows a combined determination of M⋆ and Φ⋆ with increased accuracy. Our results on the luminosity function are consistent with a small evolution of both M⋆ and Φ⋆ between z = 5 and z = 6, irrespective of the method used to derive them, either photometric redshifts applied to blindly-selected dropout samples or the classical Lyman Break Galaxy color-preselected samples. Our results lend support to higher Φ⋆ determinations at z = 6 than usually reported. The selection and combined analysis of different galaxy samples at z ≥ 7 will be presented in a forthcoming paper, as well as the evolution of the UV luminosity function between z ∼ 4.5 and 9. WUDS is intended to provide a robust database in the near-IR for the selection of targets for detailed spectroscopic studies, in particular for the EMIR/GTC GOYA Survey.
Aims. We study the dependence of galaxy clustering on luminosity and stellar mass at redshifts $z\sim$ 0.2–1, using the first 10K redshifts from the zCOSMOS spectroscopic survey of the COSMOS field. ...Methods. We measured the redshift-space correlation functions $\xi(r_{\rm p},\pi)$ and $\xi(s)$ and the projected function, $w_{\rm p}(r_{\rm p})$ for subsamples covering different luminosity, mass, and redshift ranges. We explored and quantified in detail the observational selection biases from the flux-limited nature of the survey, using ensembles of realistic semi-analytic mock samples built from the Millennium simulation. We used the same mock data sets to carefully check our covariance and error estimate techniques, comparing the performances of methods based on the scatter in the mocks and on bootstrapping schemes. We finally compared our measurements to the cosmological model predictions from the mock surveys. Results. At odds with other measurements at similar redshift and in the local Universe, we find a weak dependence of galaxy clustering on luminosity in all three redshift bins explored. A mild dependence on stellar mass is instead observed, in particular on small scales, which becomes particularly evident in the central redshift bin ($0.5<z<0.8$), where $w_{\rm p}(r_{\rm p})$ shows strong excess power on scales >1 h-1 Mpc. This is reflected in the shape of the full $\xi(r_{\rm p},\pi)$ that we interpret as produced by dominating structures almost perpendicular to the line of sight in the survey volume. Comparing to $z\sim 0$ measurements, we do not see any significant evolution with redshift of the amplitude of clustering for bright and/or massive galaxies. Conclusions. This is consistent with previous results and the standard picture in which the bias evolves more rapidly for the most massive haloes, which in turn host the highest-stellar-mass galaxies. At the same time, however, the clustering measured in the zCOSMOS 10K data at $0.5<z<1$ for galaxies with $\log(M/M_\odot)\ge 10$ is only marginally consistent with the predictions from the mock surveys. On scales larger than ~2 h-1 Mpc, the observed clustering amplitude is compatible only with ~1% of the mocks. Thus, if the power spectrum of matter is ΛCDM with standard normalisation and the bias has no “unnatural” scale-dependence, this result indicates that COSMOS has picked up a particularly rare, ~2–3σ positive fluctuation in a volume of ~106 h-1 Mpc3. These findings underline the need for larger surveys of the $z\sim 1$ Universe to appropriately characterise the level of structure at this epoch.
Context. The CoRoT - Convection Rotation and planetary Transits - space mission is a great opportunity for monitoring stars with excellent time-sampling and unprecedented photometric precision for up ...to 150 days. As an important benefit, high-quality RR Lyrae light curves are obtained with a quasi-uninterrupted coverage over several pulsation and Blazhko cycles. Aims: The Blazhko effect in RR Lyrae stars is an unsolved problem of astrophysics. We used the high-precision space data to contribute more precise knowledge to explain the possible physical processes behind the phenomenon. Methods: We applied different period-finding techniques including Period04, MuFrAn, PDM and SigSpec. Amplitude and phase modulation were investigated by an analytical function method as well as with the traditional O-C diagrams. Results: The Blazhko modulation frequency is directly detected in the spectrum, as well as its first and second harmonics. It shows the non-linear nature of the Blazhko modulation. Besides the triplets, further higher-order modulation side peaks appear around the pulsation frequency as quintuplet, septuplet, nonuplet, undecaplet, tredecaplet, quindecaplet and sepdecaplet structures. Additional frequencies, not belonging to the classical multiplet structures, are detected, as well as their linear combinations with the fundamental radial mode. We interpret these additional terms as non-radial modes. During the five consecutive Blazhko cycles, there is a shift of the maximum phase around 0.011 pulsation phase which is likely the consequence of a long term modulation.
We report the first likely spectroscopic confirmation of a $z\sim 10.0$ galaxy from our ongoing search for distant galaxies with ISAAC/VLT. Galaxy candidates at $z \ga 7$ are selected from ultra-deep ...JHKs images in the core of gravitational lensing clusters for which deep optical imaging is also available, including HST data. The object reported here, found behind Abell 1835, exhibits a faint emission line detected in the J band, leading to $z=10.0$ when identified as Lyα, in excellent agreement with the photometric redshift determination. Redshifts $z < 7$ are very unlikely for various reasons we discuss. The object is located on the critical lines corresponding to $z=9$ to 11. The magnification factor μ ranges from 25 to 100. For this object we estimate ${\it SFR}({\rm Ly}\alpha) \sim (0.8{-}2.2)~M _{\odot}$ yr-1 and ${\it SFR}({\rm UV}) \sim (47{-}75)~M _{\odot}$ yr-1, both uncorrected for lensing. The steep UV slope indicates a young object with negligible dust extinction. SED fits with young low-metallicity stellar population models yield (adopting $\mu=25$) a lensing corrected stellar mass of $M_\star \sim 8 \times 10^6~M _{\odot}$, and luminosities of $2 \times 10^{10}~L _{\odot}$, corresponding to a dark matter halo of a mass of typically $M_{\rm tot} \ga 5 \times 10^8~M _{\odot}$. In general our observations show that under excellent conditions and using strong gravitational lensing direct observations of galaxies close to the “dark ages” are feasible with ground-based 8-10 m class telescopes.
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