Structural properties of discs and bulges of early-type galaxies

We have used the EFAR sample of galaxies to study the light distributions of early-type galaxies. We decompose the 2D light distribution of the galaxies in a flattened spheroidal component with a Sersic radial light profile and an inclined disc component with an exponential light profile. We show that the brightest, bulge dominated elliptical galaxies have a fairly broad distribution in the Sersic profile shape parameter n_B, with a median of about 3.7 and a sigma of ~0.9. Other galaxies have smaller n_B values, meaning that spheroids are in general less concentrated than the n_B=4 de Vaucouleurs-law profile. The results of our light decompositions are robust, even though without kinematic information we cannot prove that the spheroids and discs are really pressure- and rotation-supported stellar systems. If we assume that the detected spheroids and discs are indeed separate components, we can draw the following conclusions: 1) the spheroid and disc scale sizes are correlated; 2) bulge-to-total luminosity ratios, bulge effective radii, and bulge n_B values are all positively correlated; 3) the bivariate space density distribution of elliptical galaxies in the (luminosity, scale size)-plane is well described by a Schechter luminosity function in and a log-normal scale-size distribution at a given luminosity; 4) at the brightest luminosities, the scale size distribution of elliptical galaxies is similar to those of bright spiral galaxies; at fainter luminosities the elliptical scale size distribution peaks at distinctly smaller sizes than the spiral galaxy distribution; and 5) bulge components of early-type galaxies are typically a factor 1.5 to 2.5 smaller than the disks of spiral galaxies, while disc components of early-type galaxies are typically twice as large as the discs of spiral galaxies. [abridged]Comment: 16 pages, 18 figures. Accepted for publication in the MNRA

The Effects of Starburst Activity on Low Surface Brightness Disk Galaxies

Although numerous simulations have been done to understand the effects of intense bursts of star formation on high surface brightness galaxies, few attempts have been made to understand how localized starbursts would affect both the color and surface brightness of low surface brightness (LSB) galaxies. To remedy this, we have run 53 simulations involving bursts of star formation activity on LSB galaxies, varying both the underlying galaxy properties and the parameters describing the starbursts. We discovered that although changing the total color of a galaxy was fairly straightforward, it was virtually impossible to alter a galaxy's central surface brightness and thereby remove it from the LSB galaxy classification without placing a high (and fairly artificial) threshold for the underlying gas density. The primary effect of large amounts of induced star formation was to produce a centralized core (bulge) component which is generally not observed in LSB galaxies. The noisy morphological appearance of LSB galaxies as well as their noisy surface brightness profiles can be reproduced by considering small bursts of star formation that are localized within the disk. The trigger mechanism for such bursts is likely distant/weak tidal encounters. The stability of disk central surface brightness to these periods of star formation argues that the large space density of LSB galaxies at z = 0 should hold to substantially higher redshifts.Comment: 38 pages, 5 figures, 4 tables, tarred and compressed Also available on http://guernsey.uoregon.edu/~kare

Testing the Hypothesis of Modified Dynamics with Low Surface Brightness Galaxies and Other Evidence

The rotation curves of low surface brightness galaxies provide a unique data set with which to test alternative theories of gravitation over a large dynamic range in size, mass, surface density, and acceleration. Many clearly fail, including any in which the mass discrepancy appears at a particular length-scale. One hypothesis, MOND [Milgrom 1983, ApJ, 270, 371], is consistent with the data. Indeed, it accurately predicts the observed behavior. We find no evidence on any scale which clearly contradicts MOND, and a good deal which supports it.Comment: Accepted for publication in the Astrophysical Journal. 35 pages AAStex + 9 figures. This result surprised the bejeepers out of us, to

1.65 micron (H-band) surface photometry of galaxies. VIII: the near-IR k-space at z=0

We present the distribution of a statistical sample of nearby galaxies in the k-space (k1 ~ log M, k2 ~ log Ie, k3 ~ log M/L). Our study is based on near-IR (H-band: lambda = 1.65 micron) observations, for the first time comprising early- and late-type systems. Our data confirm that the mean effective dynamical mass-to-light ratio M/L of the E+S0+S0a galaxies increases with increasing effective dynamical mass M, as expected from the existence of the Fundamental Plane relation. Conversely, spiral and Im/BCD galaxies show a broad distribution in M/L with no detected trend of M/L with M, the former galaxies having M/L values about twice larger than the latter, on average. For all the late-type galaxies, the M/L increases with decreasing effective surface intensity Ie, consistent with the existence of the Tully--Fisher relation. These results are discussed on the basis of the assumptions behind the construction of the k-space and their limitations. Our study is complementary to a previous investigation in the optical (B-band: lambda = 0.44 micron) and allows us to study wavelength-dependences of the galaxy distribution in the k-space. As a first result, we find that the galaxy distribution in the k1--k2 plane reproduces the transition from bulge-less to bulge-dominated systems in galaxies of increasing dynamical mass. Conversely, it appears that the M/L of late-types is higher (lower) than that of early-types with the same M in the near-IR (optical). The origins of this behaviour are discussed in terms of dust attenuation and star formation history.Comment: 11 pages, 1 Postscript table, 3 Postscript figures, accepted for publication in MNRA

The Millennium Galaxy Catalogue: the space density and surface brightness distribution(s) of galaxies

We recover the joint and individual space density and surface brightness distribution(s) of galaxies from the Millennium Galaxy Catalogue. The MGC is a local survey spanning 30.9 sq deg and probing approximately one--two mag/sq arcsec deeper than either the Two-Degree Field Galaxy Redshift Survey (2dFGRS) or the Sloan Digital Sky Survey (SDSS). The MGC contains 10,095 galaxies to B_mgc < 20 mag with 96 per cent spectroscopic completeness. We implement a joint luminosity-surface brightness step-wise maximum likelihood method to recover the bivariate brightness distribution (BBD) inclusive of most selection effects. Integrating the BBD over surface brightness we recover the following Schechter function parameters: phi* = (0.0177 +/- 0.0015) h^3 Mpc^{-3}, M_{B}* - 5 log h = (-19.60 +/- 0.04) mag and alpha =-1.13 +/- 0.02. Compared to the 2dFGRS (Norberg et al 2002) we find a consistent M* value but a slightly flatter faint-end slope and a higher normalisation, resulting in a final luminosity density j_{b_J} = (1.99 +/- 0.17) x 10^8 h L_{odot} Mpc^{-3}. The MGC surface brightness distribution is a well bounded Gaussian at the M* point with phi* = (3.5 +/- 0.1) x 10^{-2} h^3 Mpc^{-3}, mu^{e*} = (21.90 +/- 0.01) mag/sq arcsec and sigma_{ln R_e} = 0.35 +/- 0.01. The characteristic surface brightness for luminous systems is invariant to M_{B} - 5 log h ~ -19 mag faintwards of which it moves to lower surface brightness. Higher resolution (FWHM 26 mag/sq arcsec in the B-band) observations of the local universe are now essential to probe to lower luminosity and lower surface brightness levels. [abridged]Comment: Accepted for publication in MNRAS, 26 pages with 21 figures (some degraded). A full pdf version, along with MGC data release, is available from the MGC website at, http://www.eso.org/~jliske/mg

Immunogenic Mycobacterium africanum Strains Associated with Ongoing Transmission in The Gambia

In West Africa, Mycobacterium tuberculosis strains co-circulate with M. africanum, and both pathogens cause pulmonary tuberculosis in humans. Given recent findings that M. tuberculosis T-cell epitopes are hyperconserved, we hypothesized that more immunogenic strains have increased capacity to spread within the human host population. We investigated the relationship between the composition of the mycobacterial population in The Gambia, as measured by spoligotype analysis, and the immunogenicity of these strains as measured by purified protein derivative-induced interferon-γ release in ELISPOT assays of peripheral blood mononuclear cells. We found a positive correlation between strains with superior spreading capacity and their relative immunogenicity. Although our observation is true for M. tuberculosis and M. africanum strains, the association was especially pronounced in 1 M. africanum sublineage, characterized by spoligotype shared international type 181, which is responsible for 20% of all tuberculosis cases in the region and therefore poses a major public health threat in The Gambia

2MASS photometry of edge-on spiral galaxies. I. Sample and general results

A sample of edge-on spiral galaxies aimed at a study of the main structural and photometric parameters of edge-on galaxies both of early and late types is presented. The data were taken from the 2MASS in the J, H and K_s filters. The sample consists of 175 galaxies in the K_s-filter, 169 galaxies in the H-filter and 165 galaxies in the J-filter. We present bulge and disc decompositions of each galaxy image. All galaxies have been modelled with a Sersic bulge and exponential disc with the BUDDA v2.1 package. The main conclusions of our general statistical analysis of the sample are: (1) The distribution of the apparent bulge axis ratio q_b for the subsample with n < 2 can be attributed to triaxial, nearly prolate bulges that are seen from different projections, while n > 2 bulges seem to be oblate spheroids with moderate flattening. (2) For the sample galaxies, the effective radius of the bulge r_{e,b}, the disc scalelength h and the disc scaleheight z_0 are well correlated. However, there is a clear trend for the ratio r_{e,b}/h to increase with n. (3) There is a hint that the fundamental planes of discs, which links only disc parameters and the maximum rotational velocity of gas, are different for galaxies with different bulges. (4) The investigation of the Photometric Plane of sample bulges shows that the plane is not flat and has a prominent curvature towards small values of n. For bulges this fact was not noticed earlier. (5) The clear relation between the flattening of stellar discs h/z_0 and the relative mass of a spherical component, including a dark halo, is confirmed not for bulgeless galaxies but for galaxies with massive bulges. (Abridged)Comment: 20 pages, 13 figures, accepted for publication in MNRA

Scalelength of disc galaxies

We have derived disk scale lengths for 30374 non-interacting disk galaxies in all five SDSS bands. Virtual Observatory methods and tools were used to define, retrieve, and analyse the images for this unprecedentedly large sample classified as disk/spiral galaxies in the LEDA catalogue. Cross correlation of the SDSS sample with the LEDA catalogue allowed us to investigate the variation of the scale lengths for different types of disk/spiral galaxies. We further investigat asymmetry, concentration, and central velocity dispersion as indicators of morphological type, and are able to assess how the scale length varies with respect to galaxy type. We note however, that the concentration and asymmetry parameters have to be used with caution when investigating type dependence of structural parameters in galaxies. Here, we present the scale length derivation method and numerous tests that we have carried out to investigate the reliability of our results. The average r-band disk scale length is 3.79 kpc, with an RMS dispersion of 2.05 kpc, and this is a typical value irrespective of passband and galaxy morphology, concentration, and asymmetry. The derived scale lengths presented here are representative for a typical galaxy mass of $10^{10.8\pm 0.54} \rm{M}_\odot$, and the RMS dispersion is larger for more massive galaxies. Distributions and typical trends of scale lengths have also been derived in all the other SDSS bands with linear relations that indicate the relation that connect scale lengths in one passband to another. Such transformations could be used to test the results of forthcoming cosmological simulations of galaxy formation and evolution of the Hubble sequence.Comment: Accepter for publication in MNRAS (15 pages, 15 figures, and 3 tables

Identification of a Novel Mutation of CFTR Gene in a Korean Patient with Cystic Fibrosis

Cystic fibrosis (CF) is the most common lethal autosomal recessive disease in Caucasians, but rare in Asians. The mutations of cystic fibrosis transmembrane conductance regulator (CFTR) gene are responsible for CF. To date, less than 5 cases of CF have been reported and a few of them diagnosed based on the genotype of the CFTR gene in Korea. We encountered a 4-month-old Korean infant with CF and the diagnosis was confirmed by CFTR gene mutation analysis. The patient underwent surgical operation, due to meconium ileus at birth. He suffered by recurrent respiratory infections, failure to thrive, fatty liver with hepatomegaly, and cholestasis. The mutations of the CFTR gene were identified in the patient and his parents. The patient was a compound heterozygote with a nonsense mutation of c.263T>G, resulting in an amino acid change of p.Leu88X in exon 3. It was previously described in a Korean patient with CF. The other is a novel mutation; c.2089-2090insA mutation (p.Arg697LysfsX33) in exon 13. The mutation c.263T>G was inherited from his father, and the c.2089-2090insA mutation from his mother. Respiratory infection was recovered by supportive care, and cholestasis was improved slowly with sufficient feeding and supplementation of pancreatic exocrine enzymes. He is 19-month old now and shows catch-up growth. We report a novel CFTR mutation in a Korean infant with CF

Feedback and the Formation of Dwarf Galaxy Stellar Halos

Stellar population studies show that low mass galaxies in all environments exhibit stellar halos that are older and more spherically distributed than the main body of the galaxy. In some cases, there is a significant intermediate age component that extends beyond the young disk. We examine a suite of Smoothed Particle Hydrodynamic (SPH) simulations and find that elevated early star formation activity combined with supernova feedback can produce an extended stellar distribution that resembles these halos for model galaxies ranging from $v_{200}$ = 15 km s$^{-1}$ to 35 km s$^{-1}$, without the need for accretion of subhalos.Comment: 15 pages, 15 figures, accepted MNRA