arXiv subjects

L. Sodre Jr

Publications and source records attributed to L. Sodre Jr.

5 recordsLinked to original sources

arXiv2013

JPCam: A 1.2Gpixel camera for the J-PAS survey

JPCam is a 14-CCD mosaic camera, using the new e2v 9k-by-9k 10microm-pixel 16-channel detectors, to be deployed on a dedicated 2.55m wide-field telescope at the OAJ (Observatorio Astrofisico de Javalambre) in Aragon, Spain. The camera is designed to perform a Baryon Acoustic Oscillations (BAO) survey of the northern sky. The J-PAS survey strategy will use 54 relatively narrow-band (~13.8nm) filters equi-spaced between 370 and 920nm plus 3 broad-band filters to achieve unprecedented photometric red-shift accuracies for faint galaxies over ~8000 square degrees of sky. The cryostat, detector mosaic and read electronics is being supplied by e2v under contract to J-PAS while the mechanical structure, housing the shutter and filter assembly, is being designed and constructed by a Brazilian consortium led by INPE (Instituto Nacional de Pesquisas Espaciais). Four sets of 14 filters are placed in the ambient environment, just above the dewar window but directly in line with the detectors, leading to a mosaic having ~10mm gaps between each CCD. The massive 500mm aperture shutter is expected to be supplied by the Argelander-Institut fur Astronomie, Bonn. We will present an overview of JPCam, from the filter configuration through to the CCD mosaic camera. A brief outline of the main J-PAS science projects will be included.

astro-ph.IM↗

arXiv2012

Stellar populations in superclusters of galaxies

A catalogue of superclusters of galaxies is used to investigate the influence of the supercluster environment on galaxy populations, considering galaxies brighter than M$_r<$-21+5$\log$ h. Empirical spectral synthesis techniques are applied to obtain the stellar population properties of galaxies which belong to superclusters and representative values of stellar population parameters are attributed to each supercluster. We show that richer superclusters present denser environments and older stellar populations. The galaxy populations of superclusters classified as filaments and pancakes are statistically similar, indicating that the morphology of superclusters does not have a significative influence on the stellar populations. Clusters of galaxies within superclusters are also examined in order to evaluate the influence of the supercluster environment on their galaxy properties. Our results suggest that the environment affects galaxy properties but its influence should operate on scales of groups and clusters, more than on the scale of superclusters.

astro-ph.CO↗

arXiv2007

Predicting spectral features in galaxy spectra from broad-band photometry

We explore the prospects of predicting emission line features present in galaxy spectra given broad-band photometry alone. There is a general consent that colours, and spectral features, most notably the 4000 A break, can predict many properties of galaxies, including star formation rates and hence they could infer some of the line properties. We argue that these techniques have great prospects in helping us understand line emission in extragalactic objects and might speed up future galaxy redshift surveys if they are to target emission line objects only. We use two independent methods, Artifical Neural Neworks (based on the ANNz code) and Locally Weighted Regression (LWR), to retrieve correlations present in the colour N-dimensional space and to predict the equivalent widths present in the corresponding spectra. We also investigate how well it is possible to separate galaxies with and without lines from broad band photometry only. We find, unsurprisingly, that recombination lines can be well predicted by galaxy colours. However, among collisional lines some can and some cannot be predicted well from galaxy colours alone, without any further redshift information. We also use our techniques to estimate how much information contained in spectral diagnostic diagrams can be recovered from broad-band photometry alone. We find that it is possible to classify AGN and star formation objects relatively well using colours only. We suggest that this technique could be used to considerably improve redshift surveys such as the upcoming FMOS survey and the planned WFMOS survey.

astro-ph↗

arXiv2003

Can the Local Supercluster explain the low CMB multipoles?

We show that the thermal Sunyaev-Zeldovich effect caused by hot electrons in the Local Supercluster (LSC) can explain the abnormal quadrupole and octopole of the cosmic microwave background (CMB) that were measured by WMAP and COBE. The distortion needed to account for the low observed quadrupole is a spot in the direction of the LSC with a temperature decrease of order ΔT \approx - 7 μK for ν~ 20 -- 90 Ghz photons. The temperature and density of the hot gas which can generate such an effect are consistent with observations of the X-ray background. If this hypothetic foreground is subtracted from the WMAP data, we find that the amplitude of the quadrupole (l=2) is substantially increased, and that the ``planarity'' of both the quadrupole and the octopole (l=3) are weakened. For smaller scales the effect decays and, at least in our simplified model, it does not affect the angular power spectrum at l>10. Moreover, since the Sunyaev-Zeldovich effect increases the temperature of photons with frequencies above 218 GHz, observations sensitive in that range (such as PLANCK's HFI) will be able to confirm whether the LSC indeed affects the CMB.

astro-ph↗

arXiv2002

BeppoSAX observation of the cluster Abell 970

We report new results on the cluster of galaxies Abell 970 obtained from X-ray observation with BeppoSAX. Our analysis of the BeppoSAX MECS and LECS data in the range [0.15-10] keV reveals a mean cluster gas temperature of kT = 4.46_{-0.15}^{+0.14}, a metallicity of Z = 0.31_{-0.04}^{+0.05} Z_\odot, and an interstellar hydrogen absorption density column of N_H = 6.05_{-0.97}^{+1.29} 10^20 cm^-2. Moreover, we obtained azimuthally averaged radial profiles of these quantities. Our results are consistent with the hypothesis that Abell 970 has been disturbed by a past merger or by the ongoing merger process of a substructure, that put the cluster out of equilibrium. This is also demonstrated by the offset between the gas and galaxy distributions. Combining the X-ray data with a recently published analysis of new galaxy radial velocities, we conclude that a subcluster 8 arcmin to the NW is falling into Abell 970 and will merge in a few Gigayears, thus disturbing Abell 970's newly acquired equilibrium. The high alpha-elements/iron ratio that we derive for this cluster supports the hypothesis of early intracluster medium enrichment by Type II supernovae.

astro-ph↗