40 research outputs found
A Ks-band-selected catalogue of objects in the ALHAMBRA survey
The original ALHAMBRA catalogue contained over 400,000 galaxies selected using a synthetic F814W image, to the magnitude limit AB(F814W)24.5. Given the photometric redshift depth of the ALHAMBRA multiband data (=0.86) and the approximately -band selection, there is a noticeable bias against red objects at moderate redshift. We avoid this bias by creating a new catalogue selected in the band. This newly obtained catalogue is certainly shallower in terms of apparent magnitude, but deeper in terms of redshift, with a significant population of red objects at . We select objects using the band images, which reach an approximate AB magnitude limit . We generate masks and derive completeness functions to characterize the sample. We have tested the quality of the photometry and photometric redshifts using both internal and external checks. Our final catalogue includes sources down to , with a significant tail towards high redshift. We have checked that there is a large sample of objects with spectral energy distributions that correspond to that of massive, passively evolving galaxies at , reaching as far as . We have tested the possibility of combining our data with deep infrared observations at longer wavelengths, particularly Spitzer IRAC data
A review of elliptical and disc galaxy structure, and modern scaling laws
A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their
models to describe the radial distribution of stars in `nebulae'. This article
reviews the progress since then, providing both an historical perspective and a
contemporary review of the stellar structure of bulges, discs and elliptical
galaxies. The quantification of galaxy nuclei, such as central mass deficits
and excess nuclear light, plus the structure of dark matter halos and cD galaxy
envelopes, are discussed. Issues pertaining to spiral galaxies including dust,
bulge-to-disc ratios, bulgeless galaxies, bars and the identification of
pseudobulges are also reviewed. An array of modern scaling relations involving
sizes, luminosities, surface brightnesses and stellar concentrations are
presented, many of which are shown to be curved. These 'redshift zero'
relations not only quantify the behavior and nature of galaxies in the Universe
today, but are the modern benchmark for evolutionary studies of galaxies,
whether based on observations, N-body-simulations or semi-analytical modelling.
For example, it is shown that some of the recently discovered compact
elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to
appear in "Planets, Stars and Stellar
Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references
incl. many somewhat forgotten, pioneer papers. Original submission to
Springer: 07-June-201
Dynamics of Disks and Warps
This chapter reviews theoretical work on the stellar dynamics of galaxy
disks. All the known collective global instabilities are identified, and their
mechanisms described in terms of local wave mechanics. A detailed discussion of
warps and other bending waves is also given. The structure of bars in galaxies,
and their effect on galaxy evolution, is now reasonably well understood, but
there is still no convincing explanation for their origin and frequency. Spiral
patterns have long presented a special challenge, and ideas and recent
developments are reviewed. Other topics include scattering of disk stars and
the survival of thin disks.Comment: Chapter accepted to appear in Planets, Stars and Stellar Systems, vol
5, ed G. Gilmore. 32 pages, 17 figures. Includes minor corrections made in
proofs. Uses emulateapj.st
J-PLUS: The Javalambre Photometric Local Universe Survey
The Javalambre Photometric Local Universe Survey (J-PLUS) is an ongoing 12-band photometric optical survey, observing thousands of square degrees of the Northern Hemisphere from the dedicated JAST/T80 telescope at the Observatorio Astrofisico de Javalambre (OAJ). The T80Cam is a camera with a field of view of 2 deg(2) mounted on a telescope with a diameter of 83 cm, and is equipped with a unique system of filters spanning the entire optical range (3500-10 000 angstrom). This filter system is a combination of broad-, medium-, and narrow-band filters, optimally designed to extract the rest-frame spectral features (the 3700-4000 angstrom Balmer break region, H delta, Ca H+K, the G band, and the Mg b and Ca triplets) that are key to characterizing stellar types and delivering a low-resolution photospectrum for each pixel of the observed sky. With a typical depth of AB similar to 21.25 mag per band, this filter set thus allows for an unbiased and accurate characterization of the stellar population in our Galaxy, it provides an unprecedented 2D photospectral information for all resolved galaxies in the local Universe, as well as accurate photo-z estimates (at the delta z/(1 + z) similar to 0.005-0.03 precision level) for moderately bright (up to r similar to 20 mag) extragalactic sources. While some narrow-band filters are designed for the study of particular emission features ([O II]/lambda 3727, H alpha/lambda 6563) up to z < 0.017, they also provide well-defined windows for the analysis of other emission lines at higher redshifts. As a result, J-PLUS has the potential to contribute to a wide range of fields in Astrophysics, both in the nearby Universe (Milky Way structure, globular clusters, 2D IFU-like studies, stellar populations of nearby and moderate-redshift galaxies, clusters of galaxies) and at high redshifts (emission-line galaxies at z approximate to 0.77, 2.2, and 4.4, quasi-stellar objects, etc.). With this paper, we release the first similar to 1000 deg(2) of J-PLUS data, containing about 4.3 million stars and 3.0 million galaxies at r < 21 mag. With a goal of 8500 deg(2) for the total J-PLUS footprint, these numbers are expected to rise to about 35 million stars and 24 million galaxies by the end of the survey
Measurement of fast bars in a sample of early-type barred galaxies
We present surface photometry and stellar kinematics of a sample of 5 SB0
galaxies: ESO 139-G009, IC 874, NGC 1308, NGC 1440 and NGC 3412. We measured
their bar pattern speed using the Tremaine-Weinberg method, and derived the
ratio, R, of the corotation radius to the length of the bar semi-major axis.
For all the galaxies, R is consistent with being in the range from 1.0 and 1.4,
i.e. that they host fast bars. This represents the largest sample of galaxies
for which R has been measured this way. Taking into account the measured
distribution of R and our measurement uncertainties, we argue that this is
probably the true distribution of R. If this is the case, then the
Tremaine-Weinberg method finds a distribution of R which is in agreement with
that obtained by hydrodynamical simulations. We compared this result with
recent high-resolution N-body simulations of bars in cosmologically-motivated
dark matter halos,and conclude that these bars are not located inside centrally
concentrated dark matter halos.Comment: 19 pages, 10 PostScript figures, accepted for publication in MNRA
Deep spectroscopy of nearby galaxy clusters – II. The Hercules cluster
We carried out the deep spectroscopic observations of the nearby cluster
A2151 with AF2/WYFFOS@WHT. The caustic technique enables us to identify 360
members brighter than and within 1.3. We separated the
members into subsamples according to photometrical and dynamical properties
such as colour, local environment and infall time. The completeness of the
catalogue and our large sample allow us to analyse the velocity dispersion and
the luminosity functions of the identified populations. We found evidence of a
cluster still in its collapsing phase. The LF of the red population of A2151
shows a deficit of dwarf red galaxies. Moreover, the normalized LFs of the red
and blue populations of A2151 are comparable to the red and blue LFs of the
field, even if the blue galaxies start dominating one magnitude fainter and the
red LF is well represented by a single Schechter function rather than a double
Schechter function. We discuss how the evolution of cluster galaxies depends on
their mass: bright and intermediate galaxies are mainly affected by dynamical
friction and internal/mass quenching, while the evolution of dwarfs is driven
by environmental processes which need time and a hostile cluster environment to
remove the gas reservoirs and halt the star formation.Comment: Accepted for publication on MNARS, 15 pages,16 figures, 6 table
Fibre positioning algorithms for the WEAVE spectrograph
WEAVE is the next-generation wide-field optical spectroscopy facility for the William Herschel Telescope (WHT) in La Palma, Canary Islands, Spain. It is a multi-object «pick and place» fibre fed spectrograph with more than one thousand fibres, similar in concept to the Australian Astronomical Observatory's 2dF1 instrument with two observing plates, one of which is observing the sky while other is being reconfigured by a robotic fibre positioner. It will be capable of acquiring more than 10000 star or galaxy spectra a night. The WEAVE positioner concept uses two robots working in tandem in order to reconfigure a fully populated field within the expected 1 hour dwell-time for the instrument (a good match between the required exposure times and the limit of validity for a given configuration due to the effects of differential refraction). This presents additional constraints and complications for the software that determines the optimal path from one configuration to the next, particularly given the large number of fibre crossings implied by the 1000 fibre multiplex. This paper describes the algorithms and programming techniques used in the prototype implementations of the field configuration tool and the fibre positioner robot controller developed to support the detailed design of WEAVE. © 2014 SPIE