Disk Decomposition Research Articles

HST/WFPC2 morphologies and bar structures of field galaxies at 0.4 $\mathsf{<}$z$\mathsf{<}$ 1

To address how the galaxy Hubble sequence is established and what physical processes are involved, we studied morphological properties and internal structures of field galaxies in the past (). In addition to structural parameters derived from bulge+disk decomposition, Zheng et al. (2004, A&A, 421, 847) introduced color maps in recognizing galaxies and properly classified morphologies of 36 luminous infrared galaxies (LIRGs, m) ≥ 1011 ). Here we presented morphological classification of a parallel 75 non-LIRG sample. Our examination revealed that a significant fraction of the galaxies shows remarkable morphological evolution, most likely related to the present-day spiral galaxies. Comparison of the morphological properties between LIRGs and non-LIRGs shows that the LIRGs contain a higher fraction of ongoing major mergers and systems with signs of merging/interaction. This suggests that the merging process is one of the major mechanisms to trigger star formation. We found that spiral LIRGs probably host much fewer bars than spiral non-LIRGs, suggesting that a bar is not efficient in triggering violent star formation. Differing from Abraham et al. (1999, MNRAS, 308, 569), no dramatic change of the bar frequency is detected up to redshift . The bar frequency of the distant spirals is similar to (and may be higher than) the present-day spirals in the rest-frame B band. We conclude that bar-driven secular evolution is not a major mechanism to drive morphological evolution of field galaxies, especially their bulge formation, which is more likely related to multiple intense star formation episodes during which the galaxies appear as LIRGs (Hammer et al. 2005, A&A, 430, 115).

Bar-induced perturbation strengths of the galaxies in the Ohio State University Bright Galaxy Survey - I

Bar-induced perturbation strengths are calculated for a well-defined magnitude-limited sample of 180 spiral galaxies, based on the Ohio State University Bright Galaxy Survey. We use a gravitational torque method, the ratio of the maximal tangential force to the mean axisymmetric radial force, as a quantitative measure of the bar strength. The gravitational potential is inferred from an H-band light distribution by assuming that the M/L ratio is constant throughout the disc. Galaxies are deprojected using orientation parameters based on B-band images. In order to eliminate artificial stretching of the bulge, two-dimensional bar–bulge–disc decomposition has been used to derive a reliable bulge model. This bulge model is subtracted from an image, the disc is deprojected assuming it is thin, and then the bulge is added back by assuming that its mass distribution is spherically symmetric. We find that removing the artificial bulge stretch is important especially for galaxies having bars inside large bulges. We also find that the masses of the bulges can be significantly overestimated if bars are not taken into account in the decomposition. Bars are identified using Fourier methods by requiring that the phases of the main modes (m= 2, m= 4) are maintained nearly constant in the bar region. With such methods, bars are found in 65 per cent of the galaxies in our sample, most of them being classified as SB-type systems in the near-infrared by Eskridge and co-workers. We also suggest that as much as ≈70 per cent of the galaxies classified as SAB-types in the near-infrared might actually be non-barred systems, many of them having central ovals. It is also possible that a small fraction of the SAB-type galaxies have weak non-classical bars with spiral-like morphologies.

Thick disks of lenticular galaxies

Thick disks are faint and extended stellar components found around several disk galaxies including our Milky Way. The Milky Way thick disk, the only one studied in detail, contains mostly old disk stars (~10 Gyr), so that thick disks are likely to trace the early stages of disk evolution. Previous detections of thick disk stellar light in external galaxies have been originally made for early-type, edge-on galaxies but detailed 2D thick/thin disk decompositions have been reported for only a scant handful of mostly late-type disk galaxies. We present in this paper for the first time explicit 3D thick/thin disk decompositions characterising the presence and properties (eg scalelength and scaleheight) for a sample of eight lenticular galaxies by fitting 3D disk models to the data. For six out of the eight galaxies we were able to derive a consistent thin/thick disk model. The mean scaleheight of the thick disk is 3.6 times larger than that of the thin disk. The scalelength of the thick disk is about twice, and its central luminosity density between 3-10% of, the thin disk value. Both thin and thick disk are truncated at similar radii. This implies that thick disks extend over fewer scalelengths than thin disks, and turning a thin disk into a thick one requires therefore vertical but little radial heating. All these structural parameters are similar to thick disk parameters for later Hubble-type galaxies previously studied. We discuss our data in respect to present models for the origin of thick disks, either as pre- or post-thin-disk structures, providing new observational constraints.

Beyond the Galaxy Luminosity Function

AbstractWith the advent of large-scale surveys (i.e. Legacy Surveys) it is now possible to start looking beyond the galaxy luminosity function (LF) to more detailed statistical representations of the galaxy population, i.e multivariate distributions. In this review I first summarise the current state-of-play of the B-band global and cluster LFs and then briefly present two promising bivariate distributions: the luminosity–surface brightness plane (LSP) and the colour–luminosity plane (CLP). In both planes galaxy bulges and galaxy disks form marginally overlapping but distinct distributions, indicating two key formation/evolutionary processes (presumably merger and accretion). Forward progress in this subject now requires the routine application of reliable bulge–disk decomposition codes to allow independent investigation of these two key components.

PHOTOMETRIC AND MORPHOLOGICAL ANALYSIS OF UCM GALAXIES

ABSTRACT A set of 212 objects of the UCM (Universidad Complutense de Madrid) survey of emission-line galaxies (ELGs), selected from objective prism plates by the presence of H-alpha emission in their spectra, has been analysed in the Thuan & Gunn r filter. From CCD images of these UCM objects we have obtained the fundamental photometric parameters (apparent and absolute magnitudes, linear diameters) and a set of characteristic morphological parameters extracted by surface photometry techniques (parameters of bulb + disk decomposition, concentration indexes and mean surface brightnesses). From this information, we have carried out intrinsecal statistical analysis of the data in the UCM sample and extrinsecal comparison with other samples of galaxies. And specially, we have simultaneously applied, for the first time in a sample of ELGs, five morphological criteria in order to obtain the Hubble type of these galaxies. As results of this work we have obtained that the UCM survey is specially effective in the detection of ELGs smaller and less luminous than normal spirals (the median values of the UCM sample are Mr = -20.6 and D24 = 19.4 kpc) and that emission arises fundamentally from the nuclear regions of the galaxies (only 22% of the sample show emitting knots outside the nucleus). Morphologically, the UCM sample is dominated by late-type galaxies, with 66% being Sb or later. This result confirms the expected tendency of the ELGs to be advanced type galaxies due to the higher mass fraction in gas available in these systems. Specially, we have found 9 candidates to BCD (blue compact dwarf galaxy), five of them previously unknown. We have also obtained that 10% of the UCM ELGs present typical parameters of S0 types, supporting the idea that not all S0 galaxies are dead systems without prominent recent star formation, and that in the subsample of 16 UCM galaxies showing obvious signs of interactions, 25% are S0 type galaxies. Finally, we have analysed the influence of the medium in the occurence and nature of the ELGs. So, we have compared the presence of ELGs and their morphologies in a subsample of galaxies in the Coma cluster respect to the subsample of field galaxies. Then, we have found that whereas 34% of the field Zwicky galaxies are ELGs, this fraction is reduced to 9% in the Coma cluster, consistent with the known efect that the fraction of galaxies that are ELGs is much lower in high-density cluster environments than in the field due to the lower fraction of star forming gas available in these dense media. And respect to the morphology, the objective prism technique permits to reveal, inside a cluster globally dominated by E-S0 type galaxies, a population of ELGs with 71% being Sb type or later. In the future, we propose to study in others filters the subset of these UCM galaxies specially peculiar, like the BCD galaxies (candidates to low metalicity objects), irregular and interacting systems, and to continue investigating the conexion between the medium and the presence of ELGs and its influence on the morphology of these galaxies.

The distribution of light in galaxies - The edge-on spiral NGC 5907

view Abstract Citations (65) References (32) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Distribution of Light in Galaxies: The Edge-on Spiral NGC 5907 Barnaby, David ; Thronson, Harley A., Jr. Abstract We present our bulge and disk decomposition of an H-band (1.68 micron) image of the late-type, edge-on spiral NGC 5907. We model the disk radially as a decaying exponential and vertically as a sech(z) function, and we fit the bulge with a modified Hubble profile. From these fits, we find for the disk the exponential scalelength is 4.0 kpc and the exponential scaleheight is 0.34 kpc. We also find that the bulge-to-disk luminosity ratio (B/D) is 0.05. The near-infrared scale parameters are significantly smaller than those derived from optical observations, which can be explained by assuming the edge-on disk is optically thick in absorption at visual wavelengths due to dust. In addition, the scaleheight has no significant dependence on radial distance. We also find the face-on, central surface brightness of the disk in the B pass band is 21.7 mag arcsec^-2^. Thus, it appears that NGC 5907 falls into the narrow range of central surface brightness that has been observed in visual studies of spiral galaxies. Publication: The Astronomical Journal Pub Date: January 1992 DOI: 10.1086/116039 Bibcode: 1992AJ....103...41B Keywords: Brightness Distribution; Infrared Photometry; Spiral Galaxies; Astronomical Models; Calibrating; Galactic Bulge; Image Processing; Luminosity; Astrophysics; GALAXIES: PHOTOMETRY; GALAXIES: LUMINOSITY FUNCTION; GALAXIES: SPIRAL full text sources ADS | data products SIMBAD (1) NED (1)

Galactic disk WARPS

view Abstract Citations (41) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Galactic Disk WARPS Kuijken, Konrad Abstract Warped equilibrium configurations of galactic disks embedded in flattened haloes are considered. The relevant torques are calculated in their full nonlinearity, extending the results of linear-mode calculations. It is shown that for two specific examples, NGC 2841 and M33, it is possible to reproduce closely the observed warp shapes with these models. It is further demonstrated that the observed shapes of a galaxy's warp and rotation curve do not suffice to determine the disk mass uniquely, but can only provide upper limits on the disk-to-halo mass ratio. In the case of M33, this limit is about one-third of a maximal disk decomposition of the rotation curve. Qualitative differences between the linear theory and the present work are discussed. Publication: The Astrophysical Journal Pub Date: August 1991 DOI: 10.1086/170295 Bibcode: 1991ApJ...376..467K Keywords: Disk Galaxies; Galactic Structure; Galactic Evolution; Galactic Rotation; Warpage; Astrophysics; GALAXIES: INDIVIDUAL MESSIER NUMBER: M33; GALAXIES: INDIVIDUAL NGC NUMBER: NGC 2841; GALAXIES: INTERNAL MOTIONS; GALAXIES: STRUCTURE full text sources ADS | data products SIMBAD (2) NED (2)

Systematic Properties of Galaxies: Implications for Galaxy Formation

We have compiled a data base of V-band two-dimensional luminosity distribution for 261 galaxies in the Virgo and the Ursa Major regions (Watanabe 1983) using the 105-cm Schmidt telescope at the Kiso Observatory, Tokyo Astronomical Observatory. This is one of the largest collections of homogeneous surface photometry available to date, though the sample is biased for bright and large galaxies with m(V)≤14mag and/or D2 6≥2′. Among the sample galaxies we have selected some 200 certain members (V0<3500km/s) of the Virgo cluster and the Ursa Major clouds and performed various analyses on them to investigate systematic properties of galaxies. The two clusterings lie at nearly equal distance of (m-M)∼31.1 (Aaronson and Mould 1983). In the present paper we discuss the result of spheroid (bulge)/disk decomposition and velocity-luminosity relation for galaxies.

Foliations and genera of links

IN THIS paper we define a simple geometric operation, disc decomposition, which when successfully applied to a surface R in S3 implies that R is a surface of minimal genus for the oriented link L = dR, that there exists a C”, transversely oriented foliation 9 of S3 -&T(L) such that 9 I$ aN(L), R is the unique compact leaf (when R # D*), the union of the noncompact leaves fibre over S’ with fibre a connected non-compact leaf and if L is a knot, longitudinal (O-frame) surgery yields an irreducible 3-manifold. If L is a non-split oriented alternating link, link of I 9 crossings, knot of I 10 crossings, flat arborescent link (these include the pretzel knots), or fibred link then L bounds a surface which is disc decomposable. We show that the surface gotten by applying Seifert’s algorithm to an alternating projection is disc decomposable thereby giving a geometric proof of the result due independently by Murasugi [123 and Crowell[3] that such a surface has minimal genus. We give tables indicating the genera of the oriented nonalternating knots and links of < 10 and < 9 crossings respectively. The computation of the genera of the arborescent links including the disc decomposability of surfaces bounding flat ones and the decomposability of the fibres of fibred links can be found in [S] and [7]. The non-splitness condition is necessary by Novikov’s work [13].