J. A. L. Aguerri

The population of barred galaxies in the local universe - I. Detection and characterisation of bars

Context. Bars are very common in the centre of the disc galaxies, and they drive the evolution of their structure. The state-of-the-art imaging and redshift surveys of galaxies allow us to study the relationships between the properties of the bars and those of their hosts in statistically significant samples. Aims. A volume-limited sample of 2106 disc galaxies was studied to derive the bar fraction, length, and strength as a function of the morphology, size, local galaxy density, light concentration, and colour of the host galaxy. The sample galaxies were selected to not be strongly disturbed/interacting. Methods. The bar and galaxy properties were obtained by analysing the r-band images of the sample galaxies available in the Sloan Digital Sky Survey Data Release 5. Results. The bars were detected using the ellipse fitting method and Fourier analysis method. They were tested and calibrated with extensive simulations on artificial images. The ellipse fitting method was found to be more efficient in detecting bars in spiral galaxies. The fraction of barred galaxies turned out to be 45%. A bar was found in 29% of the lenticular galaxies, in 55% and 54% of the earlyand late-type spirals, respectively. The bar length (normalised by the galaxy size) of late-type spirals is shorter than in early-type or lenticular ones. A correlation between the bar length and galaxy size was found with longer bars hosted by larger galaxies. The bars of the lenticular galaxies are weaker than those in spirals. Moreover, the unimodal distribution of the bar strength found for all the galaxy types argues against a quick transition between the barred and unbarred statues. There is no difference between the local galaxy density of barred and unbarred galaxies. Besides, neither the length nor strength of the bars are correlated with the local density of the galaxy neighbourhoods. In contrast, a statistical significant difference between the central light concentration and colour of barred and unbarred galaxies was found. Bars are mostly located in less concentrated and bluer galaxies. Conclusions. These results indicate that the properties of bars are strongly related to those of their host galaxies, but do not depend on the local environment.

The effects of seeing on Sersic profiles - II. The Moffat PSF

ABSTRA C T The effects of seeing on Sersic r 1/n profile parameters are extensively studied using a Moffat function. This analytical approximation to the point spread function (PSF) is shown to provide the best fit to the PSF predicted from atmospheric turbulence theory when b , 4:765. The Moffat PSF is additionally shown to contain the Gaussian PSF as a limiting case Ob! 1U. The Moffat function is also shown to be numerically well behaved when modelling narrow PSFs in HST images. Seeing effects are computed for elliptically symmetric surface brightness distributions. The widely used assumption of circular symmetry when studying the effects of seeing on intrinsically elliptical sources is shown to produce significant discrepancies with respect to the true effects of seeing on these sources. A prescription to correct raw (observed) central intensities, effective radii, index n and mean effective surface brightness is given.

Stellar population gradients in galaxy discs from the CALIFA survey: the influence of bars

While studies of gasphase metallicity gradients in disc galaxies are common, very little has been done towards the acquisition of stellar abundance gradients in the same regions. We present here a comparative study of the stellar metallicity and age distributions in a sample of 62 nearly face-on, spiral galaxies with and without bars, using data from the CALIFA survey. We measure the slopes of the gradients and study their relation with other properties of the galaxies. We find that the mean stellar age and metallicity gradients in the disc are shallow and negative. Furthermore, when normalized to the effective radius of the disc, the slope of the stellar population gradients does not correlate with the mass or with the morphological type of the galaxies. In contrast to this, the values of both age and metallicity at similar to 2.5 scale lengths correlate with the central velocity dispersion in a similar manner to the central values of the bulges, although bulges show, on average, older ages and higher metallicities than the discs. One of the goals of the present paper is to test the theoretical prediction that non-linear coupling between the bar and the spiral arms is an efficient mechanism for producing radial migrations across significant distances within discs. The process of radial migration should flatten the stellar metallicity gradient with time and, therefore, we would expect flatter stellar metallicity gradients in barred galaxies. However, we do not find any difference in the metallicity or age gradients between galaxies with and without bars. We discuss possible scenarios that can lead to this lack of difference.

The CALIFA survey across the Hubble sequence: Spatially resolved stellar population properties in galaxies

Various different physical processes contribute to the star formation and stellar mass assembly histories of galaxies. One important approach to understanding the significance of these different processes on galaxy evolution is the study of the stellar population content of todays galaxies in a spatially resolved manner. The aim of this paper is to characterize in detail the radial structure of stellar population properties of galaxies in the nearby universe, based on a uniquely large galaxy sample, considering the quality and coverage of the data. The sample under study was drawn from the CALIFA survey and contains 300 galaxies observed with integral field spectroscopy. These cover a wide range of Hubble types, from spheroids to spiral galaxies, while stellar masses range from M_* ∼ 10^9 to 7 x 10^11 M_⨀. We apply the fossil record method based on spectral synthesis techniques to recover the following physical properties for each spatial resolution element in our target galaxies: the stellar mass surface density (μ_*), stellar extinction (A_V), light-weighted and mass-weighted ages ( _L, _M), and mass-weighted metallicity ( _M). To study mean trends with overall galaxy properties, the individual radial profiles are stacked in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd). We confirm that more massive galaxies are more compact, older, more metal rich, and less reddened by dust. Additionally, we find that these trends are preserved spatially with the radial distance to the nucleus. Deviations from these relations appear correlated with Hubble type: earlier types are more compact, older, and more metal rich for a given M-star, which is evidence that quenching is related to morphology, but not driven by mass. Negative gradients of _L are consistent with an inside-out growth of galaxies, with the largest _L gradients in Sb-Sbc galaxies. Further, the mean stellar ages of disks and bulges are correlated and with disks covering a wider range of ages, and late-type spirals hosting younger disks. However, age gradients are only mildly negative or flat beyond R∼2 HLR (half light radius), indicating that star formation is more uniformly distributed or that stellar migration is important at these distances. The gradients in stellar mass surface density depend mostly on stellar mass, in the sense that more massive galaxies are more centrally concentrated. Whatever sets the concentration indices of galaxies obviously depends less on quenching/morphology than on the depth of the potential well. There is a secondary correlation in the sense that at the same M_* early-type galaxies have steeper gradients. The μ_* gradients outside 1 HLR show no dependence on Hubble type. We find mildly negative _M gradients, which are shallower than predicted from models of galaxy evolution in isolation. In general, metallicity gradients depend on stellar mass, and less on morphology, hinting that metallicity is affected by both - the depth of the potential well and morphology/quenching. Thus, the largest _M gradients occur in Milky Way-like Sb-Sbc galaxies, and are similar to those measured above the Galactic disk. Sc spirals show flatter _M gradients, possibly indicating a larger contribution from secular evolution in disks. The galaxies from the sample have decreasing-outward stellar extinction; all spirals show similar radial profiles, independent from the stellar mass, but redder than E and S0. Overall, we conclude that quenching processes act in manners that are independent of mass, while metallicity and galaxy structure are influenced by mass-dependent processes.

A fast bar in the post-interaction galaxy NGC 1023

ABSTRACT We measured the bar pattern speed, Ω p , of the SB0 galaxy NGC 1023 usingthe Tremaine-Weinberg (1984) method with stellar-absorption slit spectroscopy. Themorphology and kinematics of the H I gas outside NGC 1023 suggest it suffered atidal interaction, sometime in the past, with one of its dwarf companions. At present,however, the optical disc is relaxed. If the disc had been stabilized by a massive darkmatter halo and formed its bar in the interaction, then the bar would have to be slow.We found Ω p = 5.0 ± 1.8 km s −1 arcsec −1 , so that the bar ends near its co-rotationradius. It is therefore rotating rapidly and must have a maximum disc.Key words: galaxies: elliptical and lenticular, cD — galaxies: haloes — galaxies:individual: NGC 1023 — galaxies: interactions — galaxies: kinematics and dynamics— galaxies: photometry 1 INTRODUCTIONStrong bars are seen in optical images of roughly 30% ofall high surface brightness (HSB) disk galaxies (Sellwood& Wilkinson 1993) and this fraction rises to 50%-75% inthe near IR (Knapen 1999; Knapen et al. 2000; Eskridgeet al. 2000). Understanding the structure and dynamics ofbarred (SB) galaxies is, therefore, an issue of some impor-tance. The principal dynamical quantity for SB galaxies isthe rotation frequency/pattern speed of the bar, Ω

Growth of galactic bulges by mergers - II. Low-density satellites

Context. Satellite accretion events have been invoked for mimicking the internal secular evolutionary processes of bulge growth. However, N-body simulations of satellite accretions have paid littl e attention to the evolution of bulge photometric parameters, to the processes driving this evolution, and to the consistency of this evolution wit h observations. Aims. We want to investigate whether satellite accretions indeed drive the growth of bulges, and whether they are consistent with global scaling relations of bulges and discs. Methods. We perform N-body models of the accretion of satellites onto disc galaxi es. A Tully-Fisher (M∝ V � TF rot ) scaling between primary and satellite ensures that density ratios, critical to the outc ome of the accretion, are realistic. We carry out a full struc tural, kinematic and dynamical analysis of the evolution of the bulge mass, bulge central concentration, and bulge-to-disc scaling relations.

Optical surface photometry of a sample of disk galaxies. II structural components

This work presents the structural decomposition of a sample of 11 disk galaxies, which span a range of different morphological types. The U, B, V, R, and I photometric information given in Paper I (color and color-index images and luminosity, ellipticity, and position-angle profiles) has been used to decide what types of components form the galaxies before carrying out the decomposition. We find and model such components as bulges, disks, bars, lenses and rings.

QUANTITATIVE MORPHOLOGY OF GALAXIES IN THE CORE OF THE COMA CLUSTER

We present a quantitative morphological analysis of 187 galaxies in a region covering the central 0.28 deg2 of the Coma Cluster. Structural parameters from the best-fitting Sersic r1/n bulge plus, where appropriate, exponential disk model, are tabulated here. This sample is complete down to a magnitude of R = 17 mag. By examining the recent compilation by Edwards et al. of galaxy redshifts in the direction of Coma, we find that 163 of the 187 galaxies are Coma Cluster members and that the rest are foreground and background objects. For the Coma Cluster members, we have studied differences in the structural and kinematic properties between early- and late-type galaxies and between the dwarf and giant galaxies. Analysis of the elliptical galaxies reveals correlations among the structural parameters similar to those previously found in the Virgo and Fornax Clusters. Comparing the structural properties of the Coma Cluster disk galaxies with disk galaxies in the field, we find evidence for an environmental dependence: the scale lengths of the disk galaxies in Coma are 30% smaller. An analysis of the kinematics shows marginal differences between the velocity distributions of elliptical galaxies with Sersic index n 2 (giants), the dwarf galaxies having a greater (cluster) velocity dispersion. Finally, our analysis of all 421 background galaxies in the catalog of Edwards et al. reveals a nonuniform distribution in redshift with contrasts in density of ~3, characterized by a void extending from ~10,000 to ~20,000 km s-1, and two dense and extended structures centered at ~20,000 and ~47,000 km s-1.

The effects of seeing on Sèrsic profiles

The effects of seeing on the parameters of the Sersic profile are studied in an analytical form using a Gaussian point spread function. The surface brightness of Sersic profiles is proportional (in magnitudes) to r1/n. The parameter n serves to classify the type of profile and is related to the central luminosity concentration. It is the parameter most affected by seeing; furthermore, the value of n that can be measured is always smaller than the real one. It is shown that the luminosity density of the Sersic profile with n less than 0.5 has a central depression, which is physically unlikely. Also, the intrinsic ellipticity of the sources has been taken into account and we show that the parameters are dependent when the effects of seeing are non-negligible. Finally, a prescription for correcting raw effective radii, central intensities and n parameters is given.

Quantitative morphological analysis of the Hubble Deep Field North and Hubble Deep Field South – I. Early‐ and late‐type luminosity–size relations of galaxies out to z∼ 1

Based on drizzled F606W and F814W images, we present quantitative structural parameters in the V-band rest-frame for all galaxies with z 0.2 x 10 10 h -2 L ○. show a moderate decrease [∼30(±10) per cent] in size [or interpreted differently, a decrease of ∼0.77(±0.30) mag in the central surface brightness] at a given luminosity. Finally, we make a comparison of our results with the infall and hierarchical models.