Nicola Caon

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 r 1/n , letting the exponent remain free rather than keeping it fixed at 1/n=1/4 as in the well-known de Vaucouleurs 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 consequences for the claimed independence of the shape of galaxy profiles with respect to the Fundamental Plane parameters

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 (Mbh)—more concentrated bulges have more massive black holes. Using C(1/3) from Trujillo, Graham, & Caon as a measure of bulge concentration, we find that log(Mbh/M☉) = 6.81(±0.95)C(1/3) + 5.03 ± 0.41. This correlation is shown to be marginally stronger (Spearmans rs = 0.91) than the relationship between the logarithm of the stellar velocity dispersion and log Mbh (Spearmans rs = 0.86) and has comparable or less scatter (0.31 dex in log Mbh, which decreases to 0.19 dex when we use only those galaxies whose supermassive black hole radii of influence are resolved and we remove one well-understood outlying data point).

On the estimation of galaxy structural parameters: the Sérsic model

This paper addresses some questions which have arisen from the use of the Sersic r1/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 also 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 is shown to be monotonically related with n. The second question concerns the curious coincidence between the form of the Fundamental Plane and the coupling between 〈I〉e and re when modelling a light profile. We explain, through a mathematical analysis of the Sersic law, why the quantity re〈I〉e0.7 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 re〈I〉e0.7∝σ0x (for any x, and where σ0 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 ratio truncated profile. We quantify (mathematically) how these parameters change as one reduces the outer radius of an r1/n profile, and reveal how these can vary substantially when n≥4.

MULTIBAND ANALYSIS OF A SAMPLE OF BLUE COMPACT DWARF GALAXIES. I. SURFACE BRIGHTNESS DISTRIBUTION, MORPHOLOGY, AND STRUCTURAL PARAMETERS

Broadband observations in B, V, R, and I have been performed for a sample of 28 galaxies cataloged as blue compact dwarf galaxies (BCDs). Our deep imaging, reaching surface brightness levels of a few percent of the sky brightness, has allowed the detection of underlying emission or low surface brightness features for a substantial fraction of the sample. In this paper we present the first results of the program: deep contour maps in the B band, surface brightness profiles, and color profiles for all the galaxies. The information derived for this sample of galaxies has allowed us to analyze the morphology and the structural components of BCDs. Over 70% of the galaxies show complex profiles that preclude fitting by a single standard law, with extra structure at high to intermediate intensity levels. In 21 galaxies of the sample, an underlying low surface brightness component has been detected.

Multiband Analysis of a Sample of Blue Compact Dwarf Galaxies. II. Spatially Resolved and Integrated Photometry

This is the second in a series of papers devoted to the study of a sample of 28 blue compact dwarf galaxies (BCDs). In the first paper, we presented the broadband observations in B, V, R, and I. Deep contour maps, surface-brightness profiles, and color profiles were used to analyze and discuss their morphology and structure. Here, we present new U-band and Hα observations. We compute isophotal and asymptotic magnitudes of the sample galaxies and total Hα fluxes. Comparison with previous works is done to assess the quality of the data available for BCDs. Finally, we produce an atlas of detailed color and Hα maps, the first systematic atlas of this kind published so far. The high quality of the data allows us to identify the different star-forming knots in the maps and to discriminate between them and the regions where star formation activity has already ceased. We supplement the atlas with a morphological description of each galaxy and group the galaxies in four classes according to the distribution of their star-forming regions.

Unveiling the Active Nucleus of Centaurus A

We report new HST WFPC2 and NICMOS observations of the center of the nearest radio galaxy Centaurus A (NGC 5128) and discuss their implications for our understanding of the active nucleus and jet. We detect the active nucleus in the near–IR (K and H) and, for the first time, in the optical (I and V), deriving the spectral energy distribution of the nucleus from the radio to X-rays. The optical and part of the near-IR emission can be explained by the extrapolation of the X-ray power law reddened by AV ∼ 14, a value consistent with other independent estimates. The 20pc-scale nuclear disk discovered by Schreier et al. (1998) is detected in the [FeII]λ1.64� m line and presents a morphology similar to that observed in Paα with a [FeII]/Paα ratio typical of low ionization Seyfert galaxies and LINERs. NICMOS 3 Paα observations in a 50 ′′ ×50 ′′ circumnuclear region suggest enhanced star formation (∼ 0.3M⊙ yr −1 ) at the edges of the putative bar seen with ISO, perhaps due to shocks driven into the gas. The light profile, reconstructed from V, H and K observations, shows that Centaurus A has a core profile with a resolved break at ∼ 4 ′′ and suggests a black–hole mass of ∼ 10 9 M⊙. A linear blue structure aligned with the radio/X–ray jet may indicate a channel of relatively low reddening in which dust has been swept away by the jet.

A survey of the interstellar medium in early-type galaxies. III. Stellar and gas kinematics

We present gaseous and stellar kinematics for 14 gas-rich early-type galaxies. Half of the sample exhibit irregular gaseous velocity profiles; gas/star counter-rotation is visible in five galaxies. We also find five counter-rotating stellar cores, while five more galaxies display inner components kinematically decoupled from the main stellar body. We interpret our results as an indication that the ionized gas is of external origin, is generally not in equilibrium, and may have been acquired recently. The merging or accretion events that brought the gas into the galaxy have also affected the stellar kinematics.

The extraordinarily bright optical afterglow of GRB 991208 and its host galaxy

Broad-band optical observations of the extraordi- narily bright optical afterglow of the intense gamma-ray burst GRB 991208 started � 2.1 days after the event and continued until 4 Apr 2000. The flux decay constant of the optical after- glow in the R-band is 2.30 ± 0.07 up to � 5 days, which

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.

Deep Near-Infrared Mapping of Young and Old Stars in Blue Compact Dwarf Galaxies

We analyze J, H, and Ks near-infrared data for nine blue compact dwarf (BCD) galaxies, selected from a larger sample that we have already studied in the optical. We present contour maps, surface brightness and color profiles, and color maps of the sample galaxies. The morphology of the BCDs in the near-infrared (NIR) has been found to be basically the same as in the optical. The inner regions of these systems are dominated by the starburst component. At low surface brightness levels the emission is due to the underlying host galaxy; the latter is characterized by red, radially constant colors and isophotes well fitted by ellipses. We derive accurate optical-NIR host galaxy colors for eight of the sample galaxies; these colors are typical of an evolved stellar population. Interestingly, optical-NIR color maps reveal the presence of a complex, large-scale absorption pattern in three of the sample galaxies. We study the applicability of the Sersic law to describe the surface brightness profiles of the underlying host galaxy and find that, because of the limited surface brightness interval over which the fit can be made, the derived Sersic parameters are very sensitive to the selected radial interval and to errors in the sky subtraction. Fitting an exponential model gives generally more stable results and can provide a useful tool to quantify the structural properties of the host galaxy and compare them with those of other dwarf classes, as well as with those of star-forming dwarfs at higher redshifts.