Función de luminosidad de galaxias tempranas

En este trabajo se estudia la función de luminosidad de galaxias tempranas (Elípticas + SO) para una muestra extraída del catálogo de galaxias brillantes APM. Este catálogo provee magnitudes aparentes Bj con precisión de 0.1 mag lo cual permite en base a corrimientos al rojo contar con una razonable muestra de magnitudes absolutas. La mayor parte de los corrimientos al rojo fueron obtenidos en el CASLEO utilizando el equipo Z-machine, los restantes corresponden a determinaciones realizadas por otros autores. La muestra total consiste en 785 galaxias tempranas. Para la función de luminosidad se adopta la forma dada por Schechter(1976): Φ(L)dL=Φ*(L/L*)*exp(-L/L*)d(L/L*). Para determinar los parámetros de forma α y M* se presenta una técnica consistente en una combinación del método de máxima probabilidad y simulaciones Montecarlo. Esta técnica permite un adecuado tratamiento de efectos sistemáticos y estimas de errores. Se discuten las implicancias cosmológicas de los parámetros encontrados.Asociación Argentina de Astronomí

Escenarios cosmológicos con distintos parámetros de densidad

Se están analizando diferentes escenarios cosmológicos con distintos parámetros de densidad compatibles con las determinaciones del espectro primordial de fluctuaciones, el contenido de material bariónico en cúmulos de galaxias y los resultados de la teoría de nucleosíntesis, el campo de velocidades peculiares de galaxias y su distribución espacial. Además, se está trabajando en la elaboración de un programa de cálculo de N-cuerpos basado en el esquema particle - mesh y que permite un tratamiento mas exacto de las interacciones partícula - partícula en escalas menores que la resolución numérica del potencial de la red.Asociación Argentina de Astronomí

The VLT LBG redshift survey – VI. Mapping H i in the proximity of z ∼ 3 LBGs with X-Shooter

We present an analysis of the spatial distribution and dynamics of neutral hydrogen gas around galaxies using new X-Shooter observations of z ∼ 2.5–4 quasars. Adding the X-Shooter data to our existing data set of high-resolution quasar spectroscopy, we use a total sample of 29 quasars alongside ∼1700 Lyman Break Galaxies (LBGs) in the redshift range 2 ≲ z ≲ 3.5. We measure the Lyα forest auto-correlation function, finding a clustering length of s0 = 0.081 ± 0.006 h−1 Mpc, and the cross-correlation function with LBGs, finding a cross-clustering length of s0 = 0.27 ± 0.14 h−1 Mpc and power-law slope γ = 1.1 ± 0.2. Our results highlight the weakly clustered nature of neutral hydrogren systems in the Lyα forest. Building on this, we make a first analysis of the dependence of the clustering on absorber strength, finding a clear preference for stronger Lyα forest absorption features to be more strongly clustered around the galaxy population, suggesting that they trace on average higher mass haloes. Using the projected and 2-D cross-correlation functions, we constrain the dynamics of Lyα forest clouds around z ∼ 3 galaxies. We find a significant detection of large-scale infall of neutral hydrogen, with a constraint on the Lyα forest infall parameter of βF = 1.02 ± 0.22

The starburst phenomenon from the optical/near-IR perspective

The optical/near-IR stellar continuum carries unique information about the stellar population in a galaxy, its mass function and star-formation history. Star-forming regions display rich emission-line spectra from which we can derive the dust and gas distribution, map velocity fields, metallicities and young massive stars and locate shocks and stellar winds. All this information is very useful in the dissection of the starburst phenomenon. We discuss a few of the advantages and limitations of observations in the optical/near-IR region and focus on some results. Special attention is given to the role of interactions and mergers and observations of the relatively dust-free starburst dwarfs. In the future we expect new and refined diagnostic tools to provide us with more detailed information about the IMF, strength and duration of the burst and its triggering mechanisms.Comment: 6 pages, 3 figures, to appear in "Starbursts: from 30 Doradus to Lyman Break Galaxies" 2005, eds. R. de Grijs and R. M. Gonzalez Delgado (Kluwer

Gemini Observations of Galaxies in Rich Early Environments (GOGREEN) I: survey description

We describe a new Large Program in progress on the Gemini North and South telescopes: Gemini Observations of Galaxies in Rich Early Environments (GOGREEN). This is an imaging and deep spectroscopic survey of 21 galaxy systems at 1 10 in halo mass. The scientific objectives include measuring the role of environment in the evolution of low-mass galaxies, and measuring the dynamics and stellar contents of their host haloes. The targets are selected from the SpARCS, SPT, COSMOS, and SXDS surveys, to be the evolutionary counterparts of today's clusters and groups. The new red-sensitive Hamamatsu detectors on GMOS, coupled with the nod-and-shuffle sky subtraction, allow simultaneous wavelength coverage over λ ∼ 0.6–1.05 μm, and this enables a homogeneous and statistically complete redshift survey of galaxies of all types. The spectroscopic sample targets galaxies with AB magnitudes z΄ < 24.25 and [3.6] μm < 22.5, and is therefore statistically complete for stellar masses M* ≳ 1010.3 M⊙, for all galaxy types and over the entire redshift range. Deep, multiwavelength imaging has been acquired over larger fields for most systems, spanning u through K, in addition to deep IRAC imaging at 3.6 μm. The spectroscopy is ∼50 per cent complete as of semester 17A, and we anticipate a final sample of ∼500 new cluster members. Combined with existing spectroscopy on the brighter galaxies from GCLASS, SPT, and other sources, GOGREEN will be a large legacy cluster and field galaxy sample at this redshift that spectroscopically covers a wide range in stellar mass, halo mass, and clustercentric radius

A Symmetry-induced Model of Elliptical Galaxy Patterns

S\'ersic (1968) generalized the de Vaucouleurs law which follows the projected (observed) one dimensional radial profile of elliptical galaxies closely and Dehnen (1993) proposed an analytical formula of the 3-dimensional light distributions whose projected line profile resembles the de Vaucouleurs law. This paper is involved to recover the Dehnen model and generalize the model to account for galaxy elliptical shapes by means of curvilinear coordinate systems and employing a symmetry principle. The symmetry principle maps an orthogonal coordinate system to a light distribution pattern. The coordinate system for elliptical galaxy patterns turns out to be the one which is formed by the complex-plane reciprocal transformation $Z=1/W$. The resulting spatial (3-dimensional) light distribution is spherically symmetric and has infinite gradient at its centre, which is called spherical-nucleus solution and is used to model galaxy central area. We can make changes of the coordinate system by cutting out some column areas of its definition domain, the areas containing the galaxy centre. The resulting spatial (3-dimensional) light distributions are axisymmetric or triaxial and have zero gradient at the centre, which are called elliptical-shape solutions and are used to model global elliptical patterns. The two types of logarithmic light distributions are added together to model full elliptical galaxy patterns. The model is a generalization of the Dehnen model. One of the elliptical-shape solutions permits realistic numerical calculation and is fitted to all R-band elliptical images from the Frei {\it et al.}(1996)'s galaxy sample. The fitting is satisfactory. This suggests that elliptical galaxy patterns can be represented in terms of a few basic parameters.Comment: 20 pages, 7 figure

Evolución de sistemas de galaxias en el modelo CDM

Se realizaron simulaciones numéricas de N-cuerpos para estudiar la evolución de sistemas de galaxias en el contexto teórico del modelo CDM (Cold Dark Matter) con la normalización impuesta por la reciente determinación de las fluctuaciones en la temperatura de la radiación de fondo. Se implementaron modelos de formación de galaxias suponiendo un enfriamiento instantáneo del gas en regiones cuyo contraste de densidad local es alto. Los modelos analizados incluyen los efectos de fusión de galaxias, la acreción de gas y la inyección de energía al medio intergaláctico debido a vientos de supernovas. Los resultados obtenidos permiten dar cuenta de la relación observacional Tully-Fisher para galaxias espirales y del extremo débil de la función de luminosidad; como así también de la aparente disminución en la eficiencia de formación de galaxias en sistemas ricos. Los modelos no sustentan la existencia de efectos sistemáticos entre la dispersión de velocidades peculiares de las galaxias y la materia oscura indicando una gran dificultad del modelo CDM para reproducir las observaciones.Asociación Argentina de Astronomí

The VLT LBG Redshift Survey – I. Clustering and dynamics of ≈1000 galaxies at z≈ 3†

We present the initial imaging and spectroscopic data acquired as part of the VLT VIMOS Lyman-break galaxy Survey. UBR (or UBVI) imaging covers five 36'x36' fields centred on bright z>3 QSOs, allowing ~21,000 2<z<3.5 galaxy candidates to be selected using the Lyman-break technique. We performed spectroscopic follow-up using VIMOS, measuring redshifts for 1020 z>2 LBGs and 10 z>2 QSOs from a total of 19 VIMOS pointings. From the galaxy spectra, we observe a 625+-510 km/s velocity offset between the ISM absorption and Ly-alpha emission line redshifts. Using the photometric and spectroscopic catalogues, we have analysed the galaxy clustering at z~3. In the photometric case, the angular correlation function, w(theta), is well fit by a double power-law with clustering scale-length, r_0 = 3.19+0.32-0.54 Mpc/h for r < 1 Mpc/h and r_0 = 4.59+0.31-0.33 Mpc/h at larger scales. Using the redshift sample we estimate the semi-projected correlation function, w_p(sigma) and find r_0 = 3.67+0.23-0.24 Mpc/h for the VLT sample and r_0 = 3.98+0.14-0.15 Mpc/h for a combined VLT+Keck sample. From the z-space correlation functions and assuming the above xi(r) models, we find that the combined VLT and Keck surveys require a galaxy velocity dispersion, ^1/2 ~ 700 km/s, higher than the ~400 km/s found by previous authors. We also measure a value for the gravitational growth rate parameter of beta(z=3) = 0.48+-0.17, implying a low value for the bias of b = 2.06+1.1-0.5. This value is consistent with the galaxy clustering amplitude which gives b = 2.22+-0.16, assuming the standard cosmology, implying that the evolution of the gravitational growth rate is also consistent with Einstein gravity. We have compared our LBG clustering amplitudes with lower redshift measurements and find that the clustering strength is not inconsistent with that of low-redshift L* spirals for simple 'long-lived' galaxy models.Comment: 27 pages, 25 figures, accepted in MNRA

The VLT LBG Redshift Survey - III. The clustering and dynamics of Lyman-break galaxies at z~3

We present a catalogue of 2135 galaxy redshifts from the VLT LBG Redshift Survey (VLRS), a spectroscopic survey of z ≈ 3 galaxies in wide fields centred on background quasi-stellar objects. We have used deep optical imaging to select galaxies via the Lyman-break technique. Spectroscopy of the Lyman-break galaxies (LBGs) was then made using the Very Large Telescope (VLT) Visible Multi-Object Spectrograph (VIMOS) instrument, giving a mean redshift of z = 2.79. We analyse the clustering properties of the VLRS sample and also of the VLRS sample combined with the smaller area Keck-based survey of Steidel et al. From the semiprojected correlation function, wp(σ), for the VLRS and combined surveys, we find that the results are well fit with a single power-law model, with clustering scale lengths of r0 = 3.46 ± 0.41 and 3.83 ± 0.24 h−1 Mpc, respectively. We note that the corresponding combined ξ(r) slope is flatter than for local galaxies at γ = 1.5–1.6 rather than γ = 1.8. This flat slope is confirmed by the z–space correlation function, ξ(s), and in the range 10 < s < 100 h−1 Mpc the VLRS shows an ≈2.5σ excess over the Λ cold dark matter (ΛCDM) linear prediction. This excess may be consistent with recent evidence for non-Gaussianity in clustering results at z ≈ 1. We then analyse the LBG z–space distortions using the 2D correlation function, ξ(σ, π), finding for the combined sample a large-scale infall parameter of β = 0.38 ± 0.19 and a velocity dispersion of ⟨w2z⟩−−−−√=420+140−160kms−1. Based on our measured β, we are able to determine the gravitational growth rate, finding a value of f(z = 3) = 0.99 ± 0.50 (or fσ8 = 0.26 ± 0.13), which is the highest redshift measurement of the growth rate via galaxy clustering and is consistent with ΛCDM. Finally, we constrain the mean halo mass for the LBG population, finding that the VLRS and combined sample suggest mean halo masses of log(MDM/M⊙) = 11.57 ± 0.15 and 11.73 ± 0.07, respectively