Radial Surface Brightness Research Articles

Dark and Baryonic Matter in Bright Spiral Galaxies. I. Near‐Infrared and Optical Broadband Surface Photometry of 30 Galaxies

We present photometrically calibrated images and surface photometry in the B, V, R, J, H, and K bands of 25, and in the g, r, and K bands of five nearby bright (B < 12.5 mag) spiral galaxies with inclinations of 30°-65° spanning the Hubble sequence from Sa to Scd. Data are from The Ohio State University Bright Spiral Galaxy Survey, the Two Micron All Sky Survey, and the Sloan Digital Sky Survey Second Data Release. Radial surface brightness profiles are extracted, and integrated magnitudes are measured from the profiles. Axis ratios, position angles, and scale lengths are measured from the near-infrared images. A one-dimensional bulge/disk decomposition is performed on the near-infrared images of galaxies with a nonnegligible bulge component, and an exponential disk is fit to the radial surface brightness profiles of the remaining galaxies.

Detection of Radial Surface Brightness Fluctuations and Color Gradients in Elliptical Galaxies with the Advanced Camera for Surveys

We study surface brightness fluctuations (SBFs) in a sample of eight elliptical galaxies using the Advanced Camera for Surveys (ACS) Wide Field Channel (WFC) data drawn from the Hubble Space Telescope archive. SBF magnitudes in the F814W bandpass and galaxy colors from F814W, F435W, and F606W images, when available, are presented. Galaxy surface brightness profiles are determined as well. We present the first SBF-broadband color calibration for the ACS WFC F814W bandpass and (relative) distance moduli estimates for seven of our galaxies. We detect and study in detail the SBF variations within individual galaxies as a probe of possible changes in the underlying stellar populations. Inspecting both the SBF and color gradients in comparison to model predictions, we argue that SBFs and SBF gradients can in principle be used for unraveling the different evolutionary paths taken by galaxies, although a more comprehensive study of this issue would be required. We confirm that the radial variation of galaxy stellar population properties is mainly connected to the presence of radial chemical abundance gradients, with the outer galaxy regions being more metal-poor than the inner ones.

Equilibrium Disk‐Bulge‐Halo Models for the Milky Way and Andromeda Galaxies

We describe a new set of self-consistent, equilibrium disk galaxy models that incorporate an exponential disk, a Hernquist model bulge, an NFW halo, and a central supermassive black hole. The models are derived from explicit distribution functions for each component, and the large number of parameters permit detailed modeling of actual galaxies. We present techniques that use structural and kinematic data such as radial surface brightness profiles, rotation curves, and bulge velocity dispersion profiles to find the best-fit models for the Milky Way and M31. Through N-body realizations of these models we explore their stability against the formation of bars. The models permit the study of a wide range of dynamical phenomenon with a high degree of realism.

Red giant branch stars as probes of stellar populations

Deep near infrared photometry of the newly discovered Galactic globular Cluster GLIMPSE-C01 is reported. We derived for the first time the metal abundance of this object from the slope of the RGB: in the scale of Zinn (as implemented in Harris 1996), in the scale of Caretta & Gratton (1997), and in the scale of Ferraro et al. (1999). The tip and the clump of the red giant branch were used to confirm the estimates of Kobulnicky et al. (2005), placing the cluster at kpc, behind mag of visual extinction. The best fit to the radial surface brightness profile with a single-mass King's model yielded a core radius arcmin, tidal radius arcmin and central concentration . Finally, we estimate the number of the “missing” globulars in the central region of the Milky Way. Based on the spatial distribution of the known clusters, and assuming radial symmetry around the Galactic center, we conclude that the Milky Way contains at least undiscovered objects. The distribution of known clusters in the bulge seem to resemble the orientation of the Milky Way bar.

UBVRandHubble Space TelescopeMid‐Ultraviolet and Near‐Infrared Surface Photometry and Radial Color Gradients of Late‐Type, Irregular, and Peculiar Galaxies

We introduce a data set of 142 mostly late-type spiral, irregular, and peculiar (interacting or merging) nearby galaxies observed in UBVR at the Vatican Advanced Technology Telescope (VATT), and we present an analysis of their radial color gradients. We confirm that nearby elliptical and early- to mid-type spiral galaxies show either no or only small color gradients, becoming slightly bluer with radius. In contrast, we find that late-type spiral, irregular, peculiar, and merging galaxies become on average redder with increasing distance from the center. The scatter in radial color gradient trends increases toward later Hubble type. As a preliminary analysis of a larger data set obtained with the Hubble Space Telescope (HST), we also analyze the color gradients of six nearby galaxies observed with NICMOS in the near-IR (H) and with WFPC2 in the mid-UV (F300W) and red (F814W). We discuss the possible implications of these results on galaxy formation and compare our nearby galaxy color gradients to those at high redshift. We present examples of images and UBVR radial surface brightness and color profiles, as well as of the tables of measurements; the full atlas and tables are published in the electronic edition only.

The Vega Debris Disk: A Surprise fromSpitzer

We present high spatial resolution mid- and far-infrared images of the Vega debris disk obtained with the Multiband Imaging Photometer for Spitzer (MIPS). The disk is well resolved and its angular size is much larger than found previously. The radius of the disk is at least 43 (330 AU), 70(543 AU), and 105 (815 AU) in extent at 24, 70 and 160 um, respectively. The disk images are circular, smooth and without clumpiness at all three wavelengths. The radial surface brightness profiles imply an inner boundary at a radius of 11+/-2 (86 AU). Assuming an amalgam of amorphous silicate and carbonaceous grains, the disk can be modeled as an axially symmetric and geometrically thin disk, viewed face-on, with the surface particle number density following an r^-1 power law. The disk radiometric properties are consistent with a range of models using grains of sizes ~1 to ~50 um. We find that a ring, containing grains larger than 180 um and at radii of 86-200 AU from the star, can reproduce the observed 850 um flux, while its emission does not violate the observed MIPS profiles. This ring could be associated with a population of larger asteroidal bodies analogous to our own Kuiper Belt. Cascades of collisions starting with encounters amongthese large bodies in the ring produce the small debris that is blown outward by radiation pressure to much larger distances where we detect its thermal emission. The dust production rate is >~10^15 g/s based on the MIPS results. This rate would require a very massive asteroidal reservoir for the dust to be produced in a steady state throughout Vega's life. Instead, we suggest that the disk we imaged is ephemeral and that we are witnessing the aftermath of a large and relatively recent collisional event, and subsequent collisional cascade.

Integral Field Spectroscopy of Faint Halos of Planetary Nebulae

We present the first integral field spectroscopy observations of the two planetary nebulae NGC 3242 and NGC 4361 with the VIMOS instrument attached to VLT-UT3. By co-adding a large number of spaxels, we reach an emission-line detection limit of 5 × 10-18 ergs cm-2 s-1 arcsec-2. In the case of NGC 3242, we succeed in determining some properties of the halo. The radial surface brightness profile in [O III] implies increasing mass loss before the formation of the planetary nebula. Traces of the mysterious rings are clearly visible. We find for the first time an apparent temperature gradient across a halo: from about 16,000 K close to the shell/halo transition to 20,000 K at the halo's outer edge. No line emission is seen in the suspected halo region of NGC 4361 down to the sensitivity limit.

Dark matter in the inner parts of barred galaxies: The data

This paper presents surface photometry (B,V, I, J, H, K) and H_alpha rotation curves of 27 isolated spiral galaxies. The final goal is to obtain the mass distribution of a sample of isolated spiral galaxies in order to model their gas kinematics. This is then compared to the observed rotation curve, to determine the necessity of a dark halo in the inner parts (Perez et al. 2004). The azimuthally averaged radial surface brightness profiles and the integrated magnitudes obtained from ellipse fitting are given for each of the sample galaxies. The ellipse fitting technique applied to the light distribution also allowed us to obtain the size of the bar, and the inclination and position angle of the outer isophotes that allow the galaxy deprojection. Using these profiles, 1-D disk-bulge decomposition was performed to obtain the disk scale-length and the bulge effective radius for the different bands. Through the fitting of a parametric function to the observed rotation curve, the maximum rotational velocity and the corresponding radius was obtained. The correlation between the bulge and disk parameters is in agreement with previous studies (de Jong 1996a; Marquez & Moles 1999; Baggett et al. 1998). Regarding the Kormendy relation (Kormendy 1977), in agreement with de Jong, no correlation between the bulge effective radius and its surface brightness is found, possibly due to the small range of bulge magnitudes covered. We find a smaller scatter in the structural relations when compared to non-isolated samples in agreement with Marquez & Moles (1999). Finally, a correlation between the disk scale-length and the bar size is observed, possibly reflecting the rapid growth of a bar.

Antitruncation of Disks in Early-Type Barred Galaxies

The disks of spiral galaxies are commonly thought to be truncated: the radial surface brightness profile steepens sharply beyond a certain radius (3-5 inner disk scale lengths). Here we present the radial brightness profiles of a number of barred S0-Sb galaxies with the opposite behavior: their outer profiles are distinctly shallower in slope than the main disk profile. We term these "antitruncations"; they are found in at least 25% of a larger sample of barred S0-Sb galaxies. There are two distinct types of antitruncations. About one-third show a fairly gradual transition and outer isophotes that are progressively rounder than the main disk isophotes, suggestive of a disk embedded within a more spheroidal outer zone—either the outer extent of the bulge or a separate stellar halo. But the majority of the profiles have rather sharp surface brightness transitions to the shallower, outer exponential profile and, crucially, outer isophotes that are not significantly rounder than the main disk; in the Sab-Sb galaxies, the outer isophotes include visible spiral arms. This suggests that the outer light is still part of the disk. A subset of these profiles are in galaxies with asymmetric outer isophotes (lopsided or one-armed spirals), suggesting that interactions may be responsible for at least some of the disklike antitruncations.

The Ages of Elliptical Galaxies from Mid‐Infrared Emission

The mid-infrared (10-20 μm) luminosity of elliptical galaxies is dominated by the integrated emission from circumstellar dust in red giant stars. As a single stellar population evolves, the rate of dusty mass loss from red giant stars decreases with time, so the mid-infrared luminosity should also decline with stellar age. To seek such a correlation, we have used archival Infrared Space Observatory (ISO) observations to determine surface brightness profiles and central fluxes at 15 μm in 17 early-type galaxies for which stellar ages have been determined from optical spectral indices. The radial surface brightness distributions at 15 μm generally follow the stellar de Vaucouleurs profile, as expected. We find that the surface brightness ratio μ15 μm/μI band is systematically higher in elliptical galaxies with ages 5 Gyr and in galaxies that exhibit evidence of recent mergers. Within the accuracy of our observations, μ15 μm/μI band shows no age dependence for ages 5 Gyr. The corresponding flux ratios F15 μm/FI band within apertures scaled to the effective radius (Re/8) are proportional to the μ15 μm/μI band ratios at larger galactic radii, indicating that no 15 μm emission is detected from central dust clouds visible in optical images in some of our sample galaxies. Emission at 15 μm is observed in noncentral massive clouds of dust and cold gas in NGC 1316, an elliptical galaxy that is thought to have had a recent merger. Recent Spitzer Space Telescope data also indicate the presence of polycyclic aromatic hydrocarbon (PAH) emission at 8 μm. Several ellipticals have extended regions of 15 μm emission that have no obvious counterparts at other frequencies.

A Starfish Preplanetary Nebula: IRAS 19024+0044

Using the Hubble Space Telescope, we have imaged the OH/IR star IRAS 19024+0044 (I19024) at 0.6, 0.8, 1.1, and 1.6 μm, as part of our surveys of candidate preplanetary nebulae. The images show a multipolar nebula of size ~3farcs7 × 2farcs3, with at least six elongated lobes emanating from the center of the nebula. Two of the lobes show limb-brightened tips having point-symmetric structure with respect to the expected location of the central star. The central region shows two dark bands southwest and northeast of a central shallow maximum that may be either two inclined dusty toroidal structures or the dense parts of a single wide, inhomogeneous, toroid. A very faint, surface brightness-limited, diffuse halo surrounds the lobes. Long-slit/echelle optical spectroscopy obtained at the Mount Palomar and Keck observatories shows a spatially compact source of Hα emission; the Hα line shows a strong, narrow, central core with very broad (±1000 km s^(-1)), weak wings, and a narrower blueshifted absorption feature signifying the presence of a ~100 km s^(-1) outflow. The spectrum is characterized by a strong, relatively featureless, continuum and lacks the strong forbidden emission lines characteristic of planetary nebulae, confirming that IRAS 19024 is a preplanetary nebula; the spectral type for the central star, although uncertain, is most likely early G. Interferometric observations of the CO J = 1-0 line emission with the Owens Valley Radio Interferometer show a marginally resolved molecular envelope (size 5farcs5 × 4farcs4) with an expansion velocity of 13 km s^(-1), resulting from the asymptotic giant granch (AGB) progenitor's dense, slow wind. We derive a kinematic distance of 3.5 kpc to I19024, based on its radial velocity. The bolometric flux is 7.3 × 10^(9-) ergs s^(-1) cm^(-2), and the luminosity 2850 L_☉. The relatively low luminosity of I19024, in comparison with stellar evolutionary models, indicates that the initial mass of its central star was ~1-1.5 M_☉. The lobes, which appear to be hollow structures with dense walls, have a total mass greater than or equal to about 0.02 M_☉. The dusty tori in the center have masses of a few times 10^(-3) M_☉. The faint halo has a power-law radial surface brightness profile with an exponent of about -3 and most likely represents the remnant spherical circumstellar envelope formed as a result of constant mass loss during the AGB phase over the past several thousand years. From the CO data we infer a molecular mass ≳ 0.025 M_☉ and an expansion age ≾ 2870 yr, giving a mass-loss rate ≳ 10^(-5) M_☉ yr^(-1). The far-infrared fluxes of I19024 indicate the presence of a large mass of dust in the nebula; from a simple model we infer the presence of cool (109 K) and warm (280 K) components of dust mass 5.7 × 10^(-4) and 1.5 × 10^(-7) M_☉. We discuss our results for I19024 in the light of past and current ideas for the dramatic transformation of the morphology and kinematics of mass-ejecta as AGB stars evolve into planetary nebulae.

Resolving the Inner Cavity of the HD 100546 Disk: A Candidate Young Planetary System?

The inner 100 AU of HD 100546 is studied via far-ultraviolet long-slit spectroscopy with the Hubble Space Telescope Space Telescope Imaging Spectrograph (STIS). The star is surrounded by reflection nebulosity, which can be traced 100 AU in the continuum, and by emission from H I Lyα, N I, Si II, and fluorescent H2 transitions. The Lyα emission can be traced up to 200 AU along the system semimajor axis and 300 AU along the semiminor axis. The radial surface brightness profile and the presence of both reflection nebulosity and molecular gas suggest that we have detected the flared surface of the disk predicted from analysis of the IR spectral energy distribution. When corrected for the r-2 falloff in illumination from the Herbig Be star, the reflection nebulosity, neutral atomic gas, and H2 emission all reveal the presence of a central cavity extending 013 ± 0025 (13 AU) from the star, more than 20 times larger in radius than would be expected from dust sublimation alone. The reflection nebulosity within the cavity is centered on a location 005 (5 AU) to the southeast of the star along the system semimajor axis. The pericenter asymmetry in the cavity is inconsistent with cavity formation by the combined effects of ice sublimation, radiation pressure blowout on small grains, or other disk chemistry that should produce azimuthally symmetric features. The STIS data are also consistent with a current accretion rate onto the Herbig Be star no higher than a few times 10-9 M☉ yr-1, an order of magnitude lower than seen in 5-8 Myr old Herbig Ae stars. The low accretion rate, large cavity, pericenter asymmetry, and deficit of warm dust grain emission observed over 2-8 μm are all consistent with dynamical sculpting of the disk by one or more bodies within the disk. An upper limit to the flux from any chromospherically active, low-mass companion is a factor of 5-10 fainter than AU Mic (M1 Ve; t = 12 Myr) at the distance of HD 100546. This upper limit firmly excludes a low-mass stellar companion within the cavity but does not exclude a less active and/or luminous brown dwarf. The absence of similar central clearing in younger Herbig Ae stars suggests that any companion must become externally detectable late in the evolution of the disk, favoring a giant planet as the source of the structure in the HD 100546 disk.

Globular Clusters with Dark Matter Halos. I. Initial Relaxation

In a series of two papers, we test the primordial scenario of globular cluster formation using results of high-resolutions N-body simulations. In this first paper we study the initial relaxation of a stellar core inside a live dark matter minihalo in the early universe. Our dark-matter dominated globular clusters show features which are usually attributed to the action of the tidal field of the host galaxy. Among them are the presence of an apparent cutoff (tidal radius) or of a break in the outer parts of the radial surface brightness profile, and a flat line-of-sight velocity dispersion profile in the outskirts of the cluster. The apparent mass-to-light ratios of our hybrid (stars + dark matter) globular clusters are very close to those of purely stellar clusters. We suggest that additional observational evidence such as the presence of obvious tidal tails is required to rule out the presence of significant amounts of dark matter in present day globular clusters.

Propagation of ionizing radiation in $\ion{H}{ii}$ regions: The effects of optically thick density fluctuations

The accepted explanation of the observed dichotomy of two orders of magnitude between in situ measurements of electron density in HII regions, derived from emission line ratios, and average measurements based on integrated emission measure, is the inhomogeneity of the ionized medium. This is expressed as a "filling factor", the volume ratio of dense to tenuous gas, measured with values of order 10^-3. Implicit in the filling factor model as normally used, is the assumption that the clumps of dense gas are optically thin to ionizing radiation. Here we explore implications of assuming the contrary: that the clumps are optically thick. A first consequence is the presence within HII regions of a major fraction of neutral hydrogen. We estimate the mean H^o/H^+ ratio for a population of HII regions in the spiral galaxy NGC 1530 to be the order of 10, and support this inference using dynamical arguments. The optically thick clumpy models allow a significant fraction of the photons generated by the ionizing stars to escape from their HII region. We show, by comparing model predictions with observations, that these models give an account at least as good as, and probably better than that of conventional models, of the radial surface brightness distribution and of selected spectral line diagnostics for physical conditions within HII regions. These models explain how an HII region can appear, from its line ratios, to be ionization bounded, yet permit a major fraction of its ionizing photons to escape.

X‐Ray Emission from the Hot Interstellar Medium and Southwest Radio Lobe of the Nearby Radio Galaxy Centaurus A

We present results from two Chandra/ACIS-I observations and one XMM-Newton observation of X-ray emission from the interstellar medium (ISM) and the inner radio lobes of the nearby radio galaxy Centaurus A. The ISM has an average radial surface brightness profile that is well described by a � -model profile with index � ¼ 0:40 � 0:04 and a temperature of kBTISM � 0:29 keV beyond 2 kpc from the nucleus. We find that diffuse X-ray emission is coincident with the outer half of the southwest radio lobe, and a bright X-ray enhancement is detected along the edge of the lobe. On the basis of energetic and lifetime arguments, we reject a nonthermal explanation for this emission. We model this emission as a thin, hot shell or cap of X-ray– emitting plasma surrounding the radio lobe that was created by the supersonic inflation of the lobe. This plasma shell is both hotter than (kBTSH � 2:9 keV) and greatly overpressurized relative to the ambient ISM, indicating supersonic expansion. We estimate that the lobe is expanding into the ISM at approximately Mach 8.5, or 2400 km s � 1 . We are not directly observing the bow shock, but rather the cooler, denser material that is accumulating ahead of the contact discontinuity. The thermal energy in the shell is a significant fraction of the thermal energy of the hot ISM, demonstrating the possibility that the hot ISM of early galaxies can be reenergized by outflows from nuclear activity. Interestingly, no similarly bright X-ray emission is detected in or along the edge of the northeast lobe, implying that there are differences in the dynamics and evolution of the kiloparsec-scale radio components. Subject headings: galaxies: active — galaxies: individual (Centaurus A, NGC 5128) — galaxies: ISM — galaxies: jets — radio continuum: galaxies — X-rays: galaxies On-line material: color figures

An Unusual Discontinuity in the X‐Ray Surface Brightness Profile of NGC 507: Evidence of an Abundance Gradient?

We present results from a 45 ks Chandra ACIS-I observation of the nearby (z = 0.01646) NGC 507 group. The X-ray surface brightness profile of the outer region of the group is well described by an isothermal β-profile consistent with earlier ROSAT observations. We find a sharp edge or discontinuity in the radial surface brightness profile 55 kpc east and southeast of NGC 507 covering an ~125° arc. At the sharpest part of the discontinuity, the surface brightness declines by a factor of ~2 over a distance of 6.9 kpc (~15''). The inner and outer gas temperatures across the discontinuity differ by only about 0.2 keV (interior and exterior gas temperatures are 1.2 and 1.4 keV, respectively). Spectral analysis indicates that there is a gradient in the elemental abundance across the discontinuity, and comparison with the low-resolution NRAO VLA Sky Survey radio maps suggests that the discontinuity is aligned with a low surface brightness radio lobe. We conclude that the appearance of this discontinuity may be the result of two phenomena: the transonic (ℳ ~ 0.75-1) expansion/inflation of the radio lobe close to our line of sight and the transport of high-abundance material from the center of the galaxy due to this expansion.

Ultraviolet‐Optical Pixel Maps of Face‐on Spiral Galaxies: Clues for Dynamics and Star Formation Histories

Ultraviolet and optical images of the face-on spiral galaxies NGC 6753 and NGC 6782 reveal regions of strong ongoing star formation that are associated with structures traced by the old stellar populations. We use these images to construct NUV-(NUV-I814) pixel color-magnitude diagrams (pCMDs) that reveal plumes of pixels with strongly varying near-ultraviolet (NUV) surface brightness and nearly constant I814 surface brightness. The plumes correspond to sharply bounded radial ranges, with (NUV-I814) at a given NUV surface brightness being bluer at larger radii. The plumes are parallel to both the reddening vector and simple model mixtures of young and old populations, thus neither reddening nor the fraction of the young population can produce the observed separation between the plumes. The images and radial surface brightness and color plots indicate that the separate plumes are caused by sharp declines in the surface densities of the old populations at radii corresponding to disk resonances. The maximum surface brightness of the NUV light remains essentially constant with radius, while the maximum I814 surface brightness declines sharply with radius. A mid-ultraviolet (MUV) image of NGC 6782 shows emission from the nuclear ring. The distribution of points in an (MUV-NUV)-(NUV-I814) pixel color-color diagram is broadly consistent with the simple mixture model but shows a residual trend that the bluest pixels in (MUV-NUV) are the reddest pixels in (NUV-I814). This may be due to a combination of red continuum from late-type supergiants and [S III] emission lines associated with H II regions in active star-forming regions. We have shown that pixel mapping is a powerful tool for studying the distribution and strength of ongoing star formation in galaxies. Deep, multicolor imaging can extend this to studies of extinction and the ages and metallicities of composite stellar populations in nearby galaxies.

Propagation velocities of gas rings in collisional ring galaxies

The propagation velocity of the first gas ring in collisional ring galaxies, i.e. the velocity at which the maximum in the radial gas density profile propagates radially in the galactic disk, is usually inferred from the radial expansion velocity of gas in the first ring. Our numerical hydrodynamics modeling of ring galaxy formation however shows that the maximum radial expansion velocity of gas in the first ring (vgas) is invariably below the propagation velocity of the first gas ring itself (). Modeling of the Cartwheel galaxy indicates that the outer ring is currently propagating at km s-1, while the maximum radial expansion velocity of gas in the outer ring is currently km s-1. The latter value is in marginal agreement with the measurements of Higdon ([CITE]) based on HI kinematics. Modeling of the radial color gradients of the Cartwheel ring galaxy also indicates that the outer ring is propagating at km s-1 for the adopted distance to the galaxy of 140 Mpc. On the other hand, the azimuthally averaged surface brightness profile of the Cartwheel's outer ring does not peak exterior to those in K- and B-bands, contrary to what would be expected for such a high propagation velocity. We show that a combined effect of 41° inclination, finite thickness, and warping of the Cartwheel's disk might be responsible for the lack of angular difference in the peak positions. Indeed, the radial surface brightness profiles obtained along the Cartwheel's major axis, where effects of inclination and finite thickness are minimized, do peak exterior to those at K- and B-bands. The angular difference in peak positions implies vring = 110 km s-1, which is in agreement with the model predictions. We briefly discuss the utility of radio continuum emission and spectral line equivalent widths for determining the propagation velocity of gas rings in collisional ring galaxies.

New insights into the photometric structure of Blue Compact Dwarf Galaxies from a deep Near-Infrared study

We present deep Near-Infrared (NIR) imaging of Blue Compact Dwarf Galaxies (BCDs), allowing for the first time to derive and systematize the NIR structural properties of their stellar low-surface brightness (LSB) host galaxies. Compared to optical data, NIR images, being less contamined by the extended stellar and ionized gas emission from the starburst, permit to study the LSB host galaxy closer to its center. We find that radial surface brightness profiles (SBPs) of the LSB hosts show at large radii a mostly exponential intensity distribution, in agreement with previous optical studies. At small to intermediate radii, however, the NIR data reveal an inwards flattening with respect to the outer exponential slope ("type V SBPs", Binggeli & Cameron 1991) in the LSB component of more than one half of the sample BCDs. This result may constitute an important observational constraint to the dynamics and evolution of BCDs. We apply a modified exponential fitting function (Papaderos et al. 1996a) to parametrize and systematically study type V profiles in BCDs. A Sersic law is found to be less suitable for studying the LSB component of BCDs, since it yields very uncertain solutions.

Surface brightness profiles and structural parameters for globular clusters in the Fornax and Sagittarius dwarf spheroidal galaxies

We present radial surface brightness profiles for all five globular clusters in the Fornax dwarf spheroidal galaxy, and for the four present members of the Sagittarius dwarf spheroidal galaxy. These profiles are derived from archival Hubble Space Telescope observations, and have been calculated using the same techniques with which we measured profiles in our previous studies of Large and Small Magellanic Cloud (LMC and SMC) clusters, apart from some small modifications. From the surface brightness profiles, we have determined structural parameters for each cluster, including core radii and luminosity and mass estimates. We also provide a brief summary of literature measurements of other parameters for these clusters, including their ages, metallicities and distances. Our core radius measurements are mostly in good agreement with those from previous lower resolution studies, although for several clusters our new values are significantly different. The profile for Fornax cluster 5 does not appear to be well fitted by a King-type model and we suggest that it is a post-core-collapse candidate. We examine the distribution of cluster core radii in each of the two dwarf galaxy systems and compare these with the distribution of core radii for old LMC clusters. The three distributions match within the limits of measurement errors and the small-sample sizes. We discuss the implications of this in the context of the radius—age trend we have previously highlighted for the Magellanic Cloud clusters.