Galaxy formation and evolution

Abstract:

Dynamical models for 17 early-type galaxies in the Coma cluster are presented. The galaxy sample consists of flattened, rotating as well as non-rotating early-types including cD and S0 galaxies with luminosities between MB = -18.79 and -22.56. Kinematical long-slit observations cover at least the major-axis and minor-axis and extend to 1-4reff. Axisymmetric Schwarzschild models are used to derive stellar mass-to-light ratios and dark halo parameters. In every galaxy, the best fit with dark matter matches the data better than the best fit without. The statistical significance is over 95 per cent for eight galaxies, around 90 per cent for five galaxies and for four galaxies it is not significant. For the highly significant cases, systematic deviations between models without dark matter and the observed kinematics are clearly seen; for the remaining galaxies, differences are more statistical in nature. Best-fitting models contain 10-50 per cent dark matter inside the half-light radius. The central dark matter density is at least one order of magnitude lower than the luminous mass density, independent of the assumed dark matter density profile. The central phase-space density of dark matter is often orders of magnitude lower than that in the luminous component, especially when the halo core radius is large. The orbital system of the stars along the major-axis is slightly dominated by radial motions. Some galaxies show tangential anisotropy along the minor-axis, which is correlated with the minor-axis Gauss-Hermite coefficient H4. Changing the balance between data-fit and regularization constraints does not change the reconstructed mass structure significantly: model anisotropies tend to strengthen if the weight on regularization is reduced, but the general property of a galaxy to be radially or tangentially anisotropic does not change. This paper is aimed to set the basis for a subsequent detailed analysis of luminous and dark matter scaling relations, orbital dynamics and stellar populations. © 2007 The Authors.

Abstract:

We present a study of the internal kinematics and stellar populations of early-type galaxies in the Fornax cluster. 10 galaxies in a luminosity range of 21.8MB17.4 were observed with the integral field units (IFU) of Gemini South GMOS and VLT-VIMOS. Velocity maps and age-metallicity diagrams are presented for NGC 1404 and NGC 1419. © 2008 Copyright International Astronomical Union 2008.

Abstract:

We determine the ensemble properties of Lyman-break galaxies (LBGs) selected as V-band dropouts to in the Chandra Deep Field-South using their rest-frame UV-to-visible spectral energy distributions. By matching the selection and performing the same analysis that has been used for samples, we show clear differences in the ensemble properties of two samples of LBGs which are separated by 1 Gyr in look-back time. We find that LBGs are typically much younger (<100 Myr) and have lower stellar masses than their counterparts (which are typically ∼ few × and ∼320 Myr old). The difference in mass is significant even when considering the presence of an older, underlying population in both samples. Such young and moderately massive systems dominate the luminous LBG population (≳70 per cent), whereas they comprise ≲30 per cent of LBG samples at. This result, which we demonstrate is robust under all reasonable modelling assumptions, shows a clear change in the properties of the luminous LBGs between and. These young and moderately massive LBGs appear to be experiencing their first (few) generations of large-scale star formation and are accumulating their first significant stellar mass. Their dominance in luminous LBG samples suggests that witnesses a period of wide-spread, recent galaxy formation. As such, LBGs are the likely progenitors of the spheroidal components of present-day massive galaxies. This is supported by their high stellar mass surface densities, and is consistent with their core phase-space densities, as well as the ages of stars in the bulge of our Galaxy and other massive systems. With implied formation redshifts of, these luminous LBGs could have only contributed to the UV photon budget at the end of reionization. However, their high star formation rates per unit area suggest these systems host outflows or winds that enrich the intragalactic and intergalactic media with metals, as has been established for LBGs. Their estimated young ages are consistent with inefficient metal-mixing on galaxy-wide scales. Therefore these galaxies may contain a significant fraction of Population III stars as proposed for LBGs by Jiminez & Haimann. © 2007 The Authors. Journal compilation © 2007 RAS.

Abstract:

Using a combination of deep MID-IR observations obtained by IRAC, MIPS and IRS on board Spitzer we investigate the MID-IR properties of Lyman Break Galaxies (LBGs) at z∼3, establish a better understanding of their nature and attempt a complete characterisation of the population. With deep mid-infrared and optical observations of ∼1000 LBGs covered by IRAC/MIPS and from the ground respectively, we extend the spectral energy distributions (SEDs) of the LBGs to mid-infrared. Spitzer data reveal for the first time that the mid-infrared properties of the population are inhomogeneous ranging from those with marginal IRAC detections to those with bright rest-frame near-infrared colors and those detected at 24m MIPS band revealing the newly discovered population of the Infrared Luminous Lyman Break Galaxies (ILLBGs). To investigate this diversity, we examine the photometric properties of the population and we use stellar population synthesis models to probe the stellar content of these galaxies. We find that a fraction of LBGs have very red colors and large estimated stellar masses M>510¹⁰M. We discuss the link between these LBGs and submm-luminous galaxies and we report the detection of rest frame 6.2 and 7.7 m emission features arising from Polycyclic Aromatic Hydrocarbons (PAH) in the Spitzer/IRS spectrum of an infrared-luminous Lyman break galaxy at z=3.01. © 2008 International Astronomical Union.