EZ: A Tool For Automatic Redshift Measurement Garilli, B.; Fumana, M.; Franzetti, P. ...
Publications of the Astronomical Society of the Pacific,
07/2010, Letnik:
122, Številka:
893
Journal Article
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We present EZ (Easy redshift), a tool we have developed within the VVDS project to help in redshift measurement from optical spectra. EZ has been designed with large spectroscopic surveys in mind, ...and in its development particular care has been given to the reliability of the results obtained in an automatic and unsupervised mode. Nevertheless, the possibility of running it interactively has been preserved, and a graphical user interface for results inspection has been designed. EZ has been successfully used within the VVDS project, as well as the zCosmos one. In this article we describe its architecture and the algorithms used, and evaluate its performances both on simulated and real data. EZ is an open-source program, freely downloadable from the Pandora Web Site.1
Context. In the last decade, astronomers have found a new type of supernova called superluminous supernovae (SLSNe) due to their high peak luminosity and long light-curves. These hydrogen-free ...explosions (SLSNe-I) can be seen to z ~ 4 and therefore, offer the possibility of probing the distant Universe. Aims. We aim to investigate the possibility of detecting SLSNe-I using ESA’s Euclid satellite, scheduled for launch in 2020. In particular, we study the Euclid Deep Survey (EDS) which will provide a unique combination of area, depth and cadence over the mission. Methods. We estimated the redshift distribution of Euclid SLSNe-I using the latest information on their rates and spectral energy distribution, as well as known Euclid instrument and survey parameters, including the cadence and depth of the EDS. To estimate the uncertainties, we calculated their distribution with two different set-ups, namely optimistic and pessimistic, adopting different star formation densities and rates. We also applied a standardization method to the peak magnitudes to create a simulated Hubble diagram to explore possible cosmological constraints. Results. We show that Euclid should detect approximately 140 high-quality SLSNe-I to z ~ 3.5 over the first five years of the mission (with an additional 70 if we lower our photometric classification criteria). This sample could revolutionize the study of SLSNe-I at z > 1 and open up their use as probes of star-formation rates, galaxy populations, the interstellar and intergalactic medium. In addition, a sample of such SLSNe-I could improve constraints on a time-dependent dark energy equation-of-state, namely w(a), when combined with local SLSNe-I and the expected SN Ia sample from the Dark Energy Survey. Conclusions. We show that Euclid will observe hundreds of SLSNe-I for free. These luminous transients will be in the Euclid data-stream and we should prepare now to identify them as they offer a new probe of the high-redshift Universe for both astrophysics and cosmology.
Context. A complex of Hα emitting blobs with strong FUV excess is associated to the dIrr galaxy VCC 1217/IC 3418 (Hester et al. 2010, ApJ, 716, L14), and extends up to 17 Kpc in the southeast ...direction. These outstanding features can be morphologically divided into diffuse filaments and compact knots, where most of the star formation activity traced by Hα takes place. Aims. We investigate the properties of the galaxy and the blobs using a multiwavelength approach to constrain their origin. Methods. We collected publicly available data in UV and Hα and observed the scene in the optical U,g,r,i bands with LBT. The photometric data allows evaluation of the star formation rate and performance of a SED fitting separately for the galaxy and the blobs in order to constrain their stellar population age. Moreover we analyzed the color and luminosity profile of the galaxy and its spectrum to investigate its recent interaction with the Virgo cluster. Results. Our analysis confirms that the most plausible mechanism for the formation of the blobs is ram pressure stripping by the Virgo cluster IGM. The galaxy colors, luminosity profile and SED are consistent with a sudden gas depletion in the last few hundred Myr. The SED fitting of the blobs constrains their ages in < 400 Myr.
Gravitational lensing has long been considered as a valuable tool to determine the total mass of galaxy clusters. The shear profile, as inferred from the statistics of ellipticity of background ...galaxies, allows us to probe the cluster intermediate and outer regions, thus determining the virial mass estimate. However, the mass sheet degeneracy and the need for a large number of background galaxies motivate the search for alternative tracers which can break the degeneracy among model parameters and hence improve the accuracy of the mass estimate. Lensing flexion, i.e. the third derivative of the lensing potential, has been suggested as a good answer to the above quest since it probes the details of the mass profile. We investigate here whether this is indeed the case considering jointly using weak lensing, magnification and flexion. We use a Fisher matrix analysis to forecast the relative improvement in the mass accuracy for different assumptions on the shear and flexion signal-to- noise (S/N) ratio also varying the cluster mass, redshift, and ellipticity. It turns out that the error on the cluster mass may be reduced up to a factor of ∼2 for reasonable values of the flexion S/N ratio. As a general result, we get that the improvement in mass accuracy is larger for more flattened haloes, but it extracting general trends is difficult because of the many parameters at play. We nevertheless find that flexion is as efficient as magnification to increase the accuracy in both mass and concentration determination.
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.
The spatial variation of the colour of a galaxy may introduce a bias in the measurement of its shape if the point spread function (PSF) profile depends on wavelength. We study how this bias depends ...on the properties of the PSF and the galaxies themselves. The bias depends on the scales used to estimate the shape, which may be used to optimize methods to reduce the bias. Here, we develop a general approach to quantify the bias. Although applicable to any weak lensing survey, we focus on the implications for the ESA Euclid mission.
Based on our study of synthetic galaxies, we find that the bias is a few times 10−3 for a typical galaxy observed by Euclid. Consequently, it cannot be neglected and needs to be accounted for. We demonstrate how one can do so using spatially resolved observations of galaxies in two filters. We show that Hubble Space Telescope (HST) observations in the F606W and F814W filters allow us to model and reduce the bias by an order of magnitude, sufficient to meet Euclid's scientific requirements. The precision of the correction is ultimately determined by the number of galaxies for which spatially resolved observations in at least two filters are available. We use results from the Millennium simulation to demonstrate that archival HST data will be sufficient for the tomographic cosmic shear analysis with the Euclid data set.
Context. For more than two decades we have known that galaxy morphological segregation is present in the Local Universe. It is important to see how this relation evolves with cosmic time. Aims. To ...investigate how galaxy assembly took place with cosmic time, we explore the evolution of the morphology-density relation up to redshift z ~ 1 using about 10 000 galaxies drawn from the zCOSMOS Galaxy Redshift Survey. Taking advantage of accurate HST/ACS morphologies from the COSMOS survey, of the well-characterised zCOSMOS 3D environment, and of a large sample of galaxies with spectroscopic redshift, we want to study here the evolution of the morphology-density relation up to z ~ 1 and its dependence on galaxy luminosity and stellar mass. The multi-wavelength coverage of the field also allows a first study of the galaxy morphological segregation dependence on colour. We further attempt to disentangle between processes that occurred early in the history of the Universe or late in the life of galaxies. Methods. The zCOSMOS field benefits of high-resolution imaging in the F814W filter from the Advanced Camera for Survey (ACS). We use standard morphology classifiers, optimised for being robust against band-shifting and surface brightness dimming, and a new, objective, and automated method to convert morphological parameters into early, spiral, and irregular types. We use about 10 000 galaxies down to IAB = 22.5 with a spectroscopic sampling rate of 33% to characterise the environment of galaxies up to z ~ 1 from the 100 kpc scales of galaxy groups up to the 100 Mpc scales of the cosmic web. The evolution of the morphology-density relation in different environments is then studied for luminosity and stellar-mass selected, volume-limited samples of galaxies. The trends are described and related to the various physical processes that could play a relevant role in the build-up of the morphology-density relation. Results. We confirm that the morphological segregation is present up to z ~ 1 for luminosity-selected, volume-limited samples. The behaviour of the morphology-density relation gets flatter at fixed masses expecially above 1010.6 $M_{\odot}$. We suggest the existence of a critical mass above which the physical processes governing galaxy stellar mass also determine the shaping of the galaxy more than its environment. We finally show that at a fixed morphology there is still a residual variation in galaxy colours with density. Conclusions. The observed evolution with redshift of the morphology-density relation offers an opportunity to trace the effect of nature and nurture as a function of environment. Even though it is based mainly on a biased view, the environmental dependence of the morphological evolution for luminosity-selected, volume-limited samples seems to indicate that nurture is in play. On the other hand, the lack of evolution observed for early-type and spiral galaxies that are more massive than 1010.8 $M_{\odot}$ independents of the environment indicates that nature has imprinted these properties early in the life of these galaxies. We conclude that the relative contribution of nature and nurture in different environments strongly depends on the mass of galaxies, consistent with a downsizing scenario.
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