Yogesh Wadadekar

MoMaF: the Mock Map Facility

We present the Mock Map Facility, a powerful tool for converting theoretical outputs of hierarchical galaxy formation models into catalogues of virtual observations. The general principle is straightforward: mock observing cones can be generated using semi-analytically post-processed snapshots of cosmological N-body simulations. These cones can then be projected to synthesize mock sky images. To this end, the paper describes in detail an efficient technique for creating such mock cones and images from the galaxies in cosmological simulations (galics) semi-analytic model, providing the reader with an accurate quantification of the artefacts it introduces at every step. We show that replication effects introduce a negative bias on the clustering signal – typically peaking at less than 10 per cent around the correlation length. We also thoroughly discuss how the clustering signal is affected by finite-volume effects, and show that it vanishes at scales larger than approximately one-tenth of the simulation box size. For the purpose of analysing our method, we show that number counts and redshift distributions obtained with galics/momaf compare well with K-band observations and the two-degree field galaxy redshift survey. Given finite-volume effects, we also show that the model can reproduce the automatic plate measuring machine angular correlation function. The momaf results discussed here are made publicly available to the astronomical community through a public data base. Moreover, a user-friendly Web interface (http://galics.iap.fr) allows any user to recover her/his own favourite galaxy samples through simple SQL queries. The flexibility of this tool should permit a variety of uses ranging from extensive comparisons between real observations and those predicted by hierarchical models of galaxy formation, to the preparation of observing strategies for deep surveys and tests of data processing pipelines.

Estimating Photometric Redshifts Using Support Vector Machines

We present a new approach to obtaining photometric redshifts using a kernel learning technique called support vector machines. Unlike traditional spectral energy distribution fitting, this technique requires a large and representative training set. When one is available, however, it is likely to produce results that are comparable to the best results obtained using template fitting and artificial neural networks. Additional photometric parameters such as morphology, size, and surface brightness can be easily incorporated. The technique is demonstrated using samples of galaxies from the Sloan Digital Sky Survey Data Release 2 and the hybrid galaxy formation code GalICS. The rms error in redshift estimation is below 0.03 for both samples. The strengths and limitations of the technique are assessed.

Star-forming Galaxies at Intermediate Redshifts: Morphology, Ages, and Sizes

We present an analysis of the deepest near-UV image obtained with the Hubble Space Telescope using the WFPC2 (F300W) as part of the parallel observations of the Hubble Ultra Deep Field campaign. The U-band 10 σ limiting magnitude measured over 0.2 arcsec2 is mAB = 27.5, which is 0.5 mag deeper than that in the Hubble Deep Field–North. We matched the U-band catalogs with those from the ACS (BViz) taken during the Great Observatories Origins Deep Survey observations of the Chandra Deep Field–South and obtained photometric redshifts for 306 matched objects. We find that the UV-selected galaxies span all the major morphological types at 0.2 100 Myr. The average half-light radius (rest-frame 1200–1800 A) of the UV-selected galaxies at 0.66 < zphot < 1.5 is 026 ± 001 (2.07 ± 0.08 kpc). The UV-selected galaxies are on average fainter (MB = -18.43 ± 0.13) than Lyman break galaxies (LBGs; MB = -23 ± 1). Our sample includes early-type galaxies that are presumably massive and forming stars only in their cores, as well as starburst-type systems that are more similar to the LBGs, although much less luminous. This implies that even the starbursts in our sample are either much less massive than LBGs or forming stars at a much lower rate, or both. The low surface brightness galaxies have no overlap with the LBGs and form an interesting new class of their own.

On the interdependence of galaxy morphology, star formation and environment in massive galaxies in the nearby Universe

Using multi-wavelength data, from UV-optical-near-mid IR, for

FAINT U-BAND DROPOUTS IN THE WFPC2 PARALLELS OF THE HUBBLE ULTRA DEEP FIELD

sim

The WFPC2 Archival Pure Parallels Project

6000 galaxies in the local Universe, we study the dependence of star formation on the morphological T-types for massive galaxies (

On the nature of infrared-faint radio sources in the Subaru X-ray Deep and Very Large Array–VIMOS VLT Deep Survey fields

log M_*/M_odot geq 10

Detection of low-metallicity warm plasma in a galaxy overdensity environment at z ∼ 0.2

). We find that, early-type spirals (Sa-Sbc) and S0s predominate in the green valley, which is a transition zone between the star forming and quenched regions. Within the early-type spirals, as we move from Sa to Sbc spirals the fraction of green valley and quenched galaxies decreases, indicating the important role of the bulge in the quenching of galaxies. The fraction of early-type spirals decreases as we enter the green valley from the blue cloud, which coincides with the increase in the fraction of S0s. This points towards the morphological transformation of early-type spiral galaxies into S0s which can happen due to environmental effects such as ram-pressure stripping, galaxy harassment, or tidal interactions. We also find a second population of S0s which are actively star-forming and are present in all environments. Since morphological T-type, specific star formation rate (sSFR), and environmental density are all correlated with each other, we compute the partial correlation coefficient for each pair of parameters while keeping the third parameter as a control variable. We find that morphology most strongly correlates with sSFR, independent of the environment, while the other two correlations (morphology-density and sSFR-environment) are weaker. Thus, we conclude that, for massive galaxies in the local Universe, the physical processes that shape their morphology are also the ones that determine their star-forming state.

Pseudo bulges in galaxy groups: the role of environment in secular evolution

We combine data from the extremely deep Hubble Space Telescope U (F300W) image, obtained using WFPC2 as part of the parallel observations of the Hubble Ultra Deep Field campaign, with BVi images from the Great Observatories Origins Deep Survey to identify a sample of Lyman break galaxies in the redshift range 2.0 z 3.5. We use recent stellar population synthesis models with a wide variety of ages, metallicities, redshifts, and dust content, and a detailed representation of the H I cosmic opacity as a function of redshift to model the colors of galaxies in our combination of WFPC2 and ACS filters. Using these models, we derive improved color selection criteria that provide a clean selection of relatively unobscured star-forming galaxies in this redshift range. Our WFPC2 F300W image is the deepest image ever obtained at that wavelength. The 10 σ limiting magnitude measured over 0.2 arcsec2 is 27.5 mag in the WFPC2 F300W image, about 0.5 mag deeper than the F300W image in the Hubble Deep Field (HDF)-North. This extra depth relative to the HDFs allows us to directly probe the luminosity function about 0.5 mag deeper than the depth accessible with the HDF data along an independent line of sight. Our sample of star-forming galaxies with 2.0 z 3.5 includes 125 objects, the majority of which show clumpy morphologies. We measure a star formation rate density of 0.18 M⊙ yr-1 Mpc-3, marginally higher than the value measured for the HDFs.

Starbursts at Intermediate Redshifts

We introduce the WFPC2 Archival Pure Parallels Project, in which the methods and procedures described here are used to obtain a near-automatic combination of WFPC2 images obtained as part of the WFPC2 Archival Parallels Program. Several techniques have been developed or refined to ensure proper alignment, registration, and combination of overlapping images that can be obtained at different times and with different orientations. We quantify the success rate and the accuracy of the registration of different types of images, and we develop techniques that are suitable to equalize the sky background without unduly affecting extended emission. About 600 combined images of the 1500 eventually planned have already been publicly released through the STScI Archive. The images released to date are especially suited to the study of star formation in the Magellanic Clouds, the stellar population in the halo of nearby galaxies, and the properties of star-forming galaxies at . z ∼ 3