On the shape of the light profiles of early-type galaxies

We have obtained the best fit to the light profiles of a luminosity limited sample of elliptical and S0 galaxies with a power law \rn, letting the exponent remain free rather than keeping it fixed at $1/n=1/4$ as in the well known \GV formula. The introduction of a free parameter in the fitting formula (ranging from $n=0.5$ for $=0.3$ kpc to $n=16$ for $=25$ kpc) is justified by the existence of a good correlation between $n$ and the global galaxian parameters, such as total luminosity and scale-radius. This result seems to be in line with the segregation of properties between the `ordinary' and `bright' families of early-type galaxies, and has consequence for the claimed independence of the shape of galaxy profiles with respect to the Fundamental Plane parameters.Comment: 10 pages, postscript file including figures, PADOVA (archived file truncated during email transfer

The Tilt of the Fundamental Plane: Three-quarters Structural Nonhomology, One-quarter Stellar Population

The variation of the mass-to-light ratios M/L of early type galaxies as function of their luminosities L is investigated. It is shown that the tilt beta=0.27 (in the B--band) of the fundamental plane relation M/L ~ L^{beta} can be understood as a combination of two effects: about one-quarter (i.e. dbeta =0.07) is a result of systematic variations of the stellar population properties with increasing luminosity. The remaining three-quarters (i.e. dbeta =0.2) can be completely attributed to nonhomology effects that lead to a systematic change of the surface brightness profiles with increasing luminosity. Consequently, the observed tilt in the K-band (beta=0.17) where stellar population effects are negligible, is explained by nonhomology effects alone. After correcting for nonhomology, the mean value of the mass-to-light ratio of elliptical galaxies (M/L_B) is 7.1+-2.8 (1 sigma scatter).Comment: 8 pages, 3 figures, ApJL, 600, 39, minor changes made to match the published versio

Analytical Galaxy Profiles for Photometric and Lensing Analysis

This article introduces a family of analytical functions of the form x^{\nu} K_{\nu}(x), where K_{\nu} is the incomplete Bessel function of the third kind. This family of functions can describe the density profile, projected and integrated light profiles and the gravitational potentials of galaxies. For the proper choice of parameters, these functions accurately approximate Sersic functions over a range of indices and are good fits to galaxy light profiles. With an additional parameter corresponding to a galaxy core radius, these functions can fit galaxy like M87 over a factor of 100,000 in radius. Unlike Sersic profiles, these functions have simple analytical 2-dimensional and 3-dimensional Fourier transforms, so they are easily convolved with spatially varying point spread function and are well suited for photometric and lensing analysis. We use these functions to estimate the effects of seeing on lensing measurements and show that high S/N measurements, even when the PSF is larger than the galaxy effective radius, should be able to recover accurate estimates of lensing distortions by weighting light in the outer isophotes that are less effected by seeing

Estudo do mecanismo da reação entre glicina e aspirina

TCC (graduação) - Universidade Federal de Santa Catarina. Centro de Ciências Físicas e Matemáticas. Curso de Química.A presença da catálise básica geral nos sistemas biológicos é importante para que uma série de reações, por exemplo as reações enzimáticas, ocorram com maior velocidade e eficiência. No caso do presente trabalho, o substrato (aspirina) é conhecido por ser um exemplo clássico de reação de hidrólise que ocorre com o auxílio de uma catálise intramolecular básica geral. O estudo realizado com a glicina consistiu na obtenção de dados físico-químicos para fornecer relações que pudessem ser consistentes para a proposta do possível mecanismo que ocorre quando a glicina reage com a aspirina na sua forma monoaniônica. Nesse sentido, foi avaliada a dependência da velocidade da reação com a concentração de glicina, o perfil da alteração da velocidade da reação de acordo com o pH do meio reacional, o efeito dos substituintes doadores e retiradores de elétrons (relação de Hammett e Jaffé) e da força do nucleófilo (relação de Brönsted), bem como o efeito isotópico cinético, utilizando meio reacional deuterado. Os dados e relações obtidos são consistentes com uma catálise intramolecular básica geral, em que o carboxilato catalisa o ataque do grupo amino da glicina ao carbono carbonílico do éster da aspirina. O estado de transição é provavelmente do tipo concertado, em que a quebra e a formação das ligações ocorrem de maneira orquestrada, sem a formação de intermediário tetraédrico

Análise do desempenho exportações chinas com base nos indicadores de competitividade externa: uma abordagem da cadeia de suprimentos

TCC (graduação) - Universidade Federal de Santa Catarina. Centro Sócio-Econômico. Economia.Este trabalho não possui resumo

A Correlation between Galaxy Light Concentration and Supermassive Black Hole Mass

We present evidence for a strong correlation between the concentration of bulges and the mass of their central supermassive black hole (M_bh) -- more concentrated bulges have more massive black holes. Using C_{r_e}(1/3) from Trujillo, Graham & Caon (2001b) as a measure of bulge concentration, we find that log (M_bh/M_sun) = 6.81(+/-0.95)C_{r_e}(1/3) + 5.03(+/-0.41). This correlation is shown to be marginally stronger (Spearman's r_s=0.91) than the relationship between the logarithm of the stellar velocity dispersion and log M_bh (Spearman's r_s=0.86), and has comparable, or less, scatter (0.31 dex in log M_bh), which decreases to 0.19 dex when we use only those galaxies whose supermassive black hole's radius of influence is resolved and remove one well understood outlying data point).Comment: 7 pages, 1 table, 2 figures. ApJ Letters, accepte

A correlation between light profile and [Mg/Fe] abundance ratio in early-type galaxies

We explore possible correlations between light profile shapes, as parameterized by the Sersic index or the concentration index C_re(1/3), and relevant stellar population parameters in early-type galaxies. Mean luminosity weighted ages, metallicities and abundance ratios were obtained from spectra of very high signal-to-noise and stellar population models that synthesize galaxy spectra at the resolution given by their velocity dispersions, in combination with an age indicator that is virtually free of the effects of metallicity. We do not find any significant correlation between the Sersic index (or C_re(1/3)) and mean age or metallicity, but a strong positive correlation of the shape parameters with [Mg/Fe] abundance ratio. This dependence is as strong as the [Mg/Fe] vs. velocity dispersion and C_re(1/3) vs. velocity dispersion relations. We speculate that early-type galaxies settle up their structure on time-scales in agreement with those imposed by their [Mg/Fe] ratios. This suggest that the global structure of larger galaxies, with larger [Mg/Fe] ratios and shorter time-scales, was already at place at high z, without experiencing a significant time evolution.Comment: 5 pages, 3 figures (to appear in The Astrophysical Journal Letters

On the estimation of galaxy structural parameters: the Sersic Model

This paper addresses some questions which have arisen from the use of the S\'ersic r^{1/n} law in modelling the luminosity profiles of early type galaxies. The first issue deals with the trend between the half-light radius and the structural parameter n. We show that the correlation between these two parameters is not only real, but is a natural consequence from the previous relations found to exist between the model-independent parameters: total luminosity, effective radius and effective surface brightness. We also define a new galaxy concentration index which is largely independent of the image exposure depth, and monotonically related with n. The second question concerns the curious coincidence between the form of the Fundamental Plane and the coupling between _e and r_e when modelling a light profile. We explain, through a mathematical analysis of the S\'ersic law, why the quantity r_e_e^{0.7} appears almost constant for an individual galaxy, regardless of the value of n (over a large range) adopted in the fit to the light profile. Consequently, Fundamental Planes of the form r_e_e^{0.7} propto sigma_0^x (for any x, and where sigma_0 is the central galaxy velocity dispersion) are insensitive to galaxy structure. Finally, we address the problematic issue of the use of model-dependent galaxy light profile parameters versus model-independent quantities for the half-light radii, mean surface brightness and total galaxy magnitude. The former implicitly assume that the light profile model can be extrapolated to infinity, while the latter quantities, in general, are derived from a signal-to-noise truncated profile. We quantify (mathematically) how these parameters change as one reduces the outer radius of an r^{1/n} profile, and reveal how these can vary substantially when n>4.Comment: 10 pages, 10 figures, accepted for publication in MNRA

Galaxy Light Concentration. I. Index stability and the connection with galaxy structure, dynamics, and supermassive black holes

We explore the stability of different galaxy light concentration indices as a function of the outermost observed galaxy radius. With a series of analytical light-profile models, we show mathematically how varying the radial extent to which one measures a galaxy's light can strongly affect the derived galaxy concentration. The "mean concentration index", often used for parameterizing high-redshift galaxies, is shown to be horribly unstable, even when modeling one-component systems such as elliptical, dwarf elliptical and pure exponential disk galaxies. The C_31 concentration index performs considerably better but is also heavily dependent on the radial extent, and hence exposure depth, of any given galaxy. We show that the recently defined central concentration index is remarkably stable against changes to the outer radius, providing a meaningful and reliable estimate of galaxy concentration. The index n from the r^(1/n) models is shown to be monotonically related with the central concentration of light, giving the index n a second and perhaps more tangible meaning. With a sample of elliptical and dwarf elliptical galaxies, we present correlations between the central light concentration and the global parameters: luminosity (Pearson's r = -0.82), effective radius (r = 0.67), central surface brightness (r = -0.88), and velocity dispersion (r = 0.80). The more massive elliptical galaxies are shown to be more centrally concentrated. We speculate that the physical mechanism behind the recently observed correlation between the central velocity dispersion (mass) of a galaxy and the mass of its central supermassive black hole may be connected with the central galaxy concentration. That is, we hypothesize that it may not simply be the amount of mass in a galaxy but rather how that mass is distributed that controls the mass of the central black hole.Comment: (aastex, 18 pages including 13 figures