Spiral Galaxies Research Papers - Academia.edu (original) (raw)

2025, Monthly Notices of the Royal Astronomical Society

We have extended our Hα objective prism survey of eight low-redshift clusters (viz. Abell 262, 347, 400, 426, 569, 779, 1367 and 1656) to include a complete sample of early-type galaxies within 1.5 Abell radii of the cluster centres. Of the 379 galaxies surveyed, 3 per cent of E, E-S0 galaxies, 6 per cent of S0 galaxies, and 9 per cent of S0/a galaxies were detected in emission. From a comparison of cluster and supercluster field galaxies, we conclude that the frequency of emission-line galaxies (ELGs; W λ 20 Å) is similar for field and cluster early-type galaxies. A similar result has previously been obtained for galaxies of types Sa and later. Together, these results confirm the inference of Biviano et al. that the relative frequency of ELGs in clusters and the field can be entirely accounted for by the different mix of morphological types between the differing environments, and that, for galaxies of a given morphological type, the fraction of ELGs is independent of environment. Detected emission is classified as 'compact' or 'diffuse', identified as circumnuclear starburst or active galactic nucleus (AGN) emission and disc emission, respectively. By comparing spectroscopic data for cluster early-type ELGs with data for field galaxies from the Palomar spectroscopic survey of nearby galactic nuclei, we demonstrate that there is modest evidence for an enhancement of compact H II emission relative to AGN emission in the early-type cluster ELGs as compared to the field. For the cluster earlytype galaxies, compact H II emission correlates strongly with a disturbed morphology. This suggests that, as for later-type cluster galaxies, this enhanced compact H II emission can readily be explained as an enhancement of circumnuclear starburst emission due to gravitational tidal interactions, most likely caused by subcluster merging and other on-going processes of cluster virialization.

2025

We propose that the pitch angle of spiral arms in disk galaxies encodes the cosmological expansion rate at the epoch of galaxy formation. By modeling spiral structure as a geodesic inflow determined by the balance of gravitational binding and cosmic expansion, we derive a direct mapping between spiral pitch angle and the Hubble parameter H(z). Applying this framework to a sample of nearby galaxies with known pitch angles, we infer consistent formation redshifts of z ≈ 10, corresponding to t ≈ 150 Myr after the Big Bang. These results suggest that spiral arms serve as fossil records of early-universe conditions, offering a novel chronometric tool for galaxy formation and a new observational window into the expansion history of the universe.

2025, Astronomy and Astrophysics Supplement Series

We present observations of the 12 CO(J =1-0) line at 2.6 mm of 65 galaxies located in the Coma supercluster region: 33 actually belong to the Coma supercluster while 32 are either foreground or background objects. These data have been obtained using the NRAO 12 m telescope at Kitt Peak (United States), and for four galaxies, using the IRAM 30 m telescope at Pico Veleta (Spain). Out of these 65 galaxies, 54 had never been observed in the CO(1-0) line; 49 have been detected by us, of which 37 are new detections. We give molecular gas masses deduced from the CO line integrated intensities, and upper limits for the 16 undetected objects, computed with a Galactic conversion factor N (H2) = 2.3 10 20 I(CO) and H0 = 75 km/s/Mpc.

2025

Perspective → Spiral • Perspective represents our perceptual viewpoint that naturally spirals outward from our center of awareness • As consciousness expands, it moves in a spiral pattern, encompassing wider views while maintaining connection to center • The spiral nature of perspective allows for recurring revisitation of ideas at deeper levels of understanding Spiral → Pattern • Spirals inherently generate recognizable patterns through their mathematical properties ( credit to CHRISTOPHER Br. CYREK)

2025

VI. FIELD CASCADE FROM BIMETRIC HOLOGRAPHY TO UNIFIED FIELD DYNAMICS

authors DEREK JORDAN BURKEEN CHRISTOPHER Br. CYREK DUSTIN HANLEY DR. JAMES MONTGOMERY LOCKWOOD

2025, elkassaoui najlae

this paper presents an overview of galaxies focusing on their classification and the anatomy of a galaxy this work aims to simplify the complex nature of a galaxy

2025, The Astronomical Journal

The KPNO International Spectroscopic Survey (KISS) is a new objective-prism survey for extragalactic emission-line objects. It combines many of the features of previous slitless spectroscopic surveys that were carried out with Schmidt telescopes using photographic plates with the advantages of modern CCD detectors. It is the first purely digital objective-prism survey, and extends previous photographic surveys to substantially fainter flux limits. In this, the first paper in the series, we give an overview of the survey technique, describe our data processing procedures, and present examples of the types of objects found by KISS. Our first Hα-selected survey list detects objects at the rate of 18.1 per square degree, which is 181 times higher than the surface density of the Markarian survey. Since the sample is line-selected, there is an imposed redshift limit of z < ∼ 0.095 due to the filter employed for the objective-prism observations. We evaluate the quality of the observed parameters derived from the survey data, which include accurate astrometry, photometry, redshifts, and line fluxes. Finally, we describe some of the many applications the KISS database will have for addressing specific questions in extragalactic astronomy. Subsequent papers in this series will present our survey lists of emission-line galaxy candidates.

2025, The Astronomical Journal

The KPNO International Spectroscopic Survey (KISS) is a new objective-prism survey for extragalactic emission-line objects. It combines many of the features of previous slitless spectroscopic surveys with the advantages of modern CCD detectors, and is the first purely digital objective-prism survey for emission-line galaxies. Here we present the first list of emission-line galaxy candidates selected from our red spectral data, which cover the spectral range 6400 to 7200 Å. In most cases, the detected emission line is Hα. The current survey list covers a one-degree-wide strip located at δ(1950) = 29 • 30 ′ and spanning the RA range 12 h 15 m to 17 h 0 m . An area of 62.2 deg 2 is covered. A total of 1128 candidate emission-line objects have been selected for inclusion in the survey list (18.1 per deg 2 ). We tabulate accurate coordinates and photometry for each source, as well as estimates of the redshift and emission-line flux and equivalent width based on measurements of the digital objective-prism spectra. The properties of the KISS emission-line galaxies are examined using the available observational data.

2025, The Astronomical Journal

The KPNO International Spectroscopic Survey (KISS) is an objective-prism survey designed to detect extragalactic emission-line objects. It combines many of the features of previous slitless spectroscopic surveys with the advantages of modern CCD detectors, and is the first purely digital objectiveprism survey for emission-line galaxies (ELGs). Here we present the third list of ELG candidates selected from our red spectral data, which cover the wavelength range 6400 to 7200 Å. In most cases, the detected emission line is Hα. The current survey list covers the region of the NOAO Deep Wide-Field Survey (NDWFS). This survey covers two fields; the first is 3 × 3 degrees square and located at RA = 14 h 30 m , δ = 34 • 30 ′ (B1950), the second is 2.3 × 4.0 degrees and centered at RA = 2 h 7.5 m , δ = -4 • 44 ′ . A total area of 19.65 deg 2 is covered by the KISS data. A total of 261 candidate emissionline objects have been selected for inclusion in the survey list (13.3 per deg 2 ). We tabulate accurate coordinates and photometry for each source, as well as estimates of the redshift, emission-line flux and line equivalent width based on measurements of the digital objective-prism spectra. The properties of the KISS ELGs are examined using the available observational data. When combined with the wealth of multi-wavelength data already available for the NDWFS fields, the current list of KISS ELGs should provide a valuable tool for studying star-formation and nuclear activity in galaxies in the local universe.

2025, EPJ Web of Conferences

2025, The Astrophysical Journal

It is generally believed that O stars, confined near the galactic midplane, are somehow able to photoionize a significant fraction of what is termed the "diffuse ionized gas" (DIG) of spiral galaxies, which can extend up to 1-2 kpc above the galactic midplane. The heating of the DIG remains poorly understood, however, as simple photoionization models do not reproduce the observed line ratio correlations well or the DIG temperature. We present turbulent mixing layer models in which warm photoionized condensations are immersed in a hot supersonic wind. Turbulent dissipation and mixing generate an intermediate region where the gas is accelerated, heated and mixed. The emission spectrum of such layers are compared with observations of Rand (ApJ 462, 712) of the DIG in the edge-on spiral NGC 891. We generate two sequence of models that fit the line ratio correlations between [S ii]/Hα, [O i]/Hα, [N ii]/[S ii] and [O iii]/Hβ reasonably well. In one sequence of models the hot wind velocity increases while in the other the ionization parameter and layer opacity increases. Despite the success of the mixing layer models, the overall efficiency in reprocessing the stellar UV is much too low, much less than 1%, which compels us to reject the TML model in its present form.

2025

Galaxy surveys targeting emission lines are characterizing the evolution of star-forming galaxies, but there is still little theoretical progress in modelling their physical properties. We predict nebular emission from star-forming galaxies within a cosmological galaxy formation model. Emission lines are computed by combining the semi-analytical model SAG with the photoionization code MAPPINGS-III. We characterize the interstellar medium of galaxies by relating the ionization parameter of gas in galaxies to their cold gas metallicity, obtaining a reasonable agreement with the observed Hα, [O II] λ3727, [O III] λ5007 luminosity functions, and the BPT diagram for local star-forming galaxies. The average ionization parameter is found to increase towards low star formation rates and high redshifts, consistent with recent observational results. The predicted link between different emission lines and their associated star formation rates is studied by presenting scaling relations to relate them. Our model predicts that emission-line galaxies have modest clustering bias, and thus reside in dark matter haloes of masses below M halo 10 12 [h -1 M ]. Finally, we exploit our modelling technique to predict galaxy number counts up to z ∼ 10 by targeting far-infrared emission lines detectable with submillimetre facilities.

2025, Monthly Notices of the Royal Astronomical Society

We used the interferometric visibility data to estimate angular diameter sizes for the supernova by model fitting. Our data nominally suggests a relatively strong deceleration for the expansion of SN 2001gd, but we cannot dismiss the possibility of a free supernova expansion. From our VLBI observations on 8 April 2003, we inferred a minimum total energy in relativistic particles and magnetic fields in the supernova shell of E min =(0.3-14) × 10 47 ergs, and a corresponding equipartition average magnetic field of B min = (50-350) mG. We also present multiwavelength VLA measurements of SN 2001gd made at our second VLBI epoch at the frequencies of 1.4, 4.9, 8.4, 15.0, 22.5, and 43.3 GHz. The VLA data are well fit by an optically thin, synchrotron spectrum (α = -1.0 ± 0.1; S ν ∝ ν α ), partially absorbed by thermal plasma. We obtain a supernova flux density of (1.02±0.05) mJy at the observing frequency of 8.4 GHz for the second epoch, which results in an isotropic radio luminosity of (6.0±0.3)× 10 36 ergs s -1 between 1.4 and 43.3 GHz, at an adopted distance of 13.1 Mpc. Finally, we report on an XMM-Newton X-ray detection of SN 2001gd on 18 December 2002. The supernova X-ray spectrum is consistent with optically thin emission from a soft component (associated with emission from the reverse shock) at a temperature around 1 keV. The observed flux corresponds to an isotropic X-ray luminosity of L X = (1.4 ± 0.4) × 10 39 ergs s -1 in the 0.3-5 keV band. We suggest that both radio and X-ray observations of SN 2001gd indicate that a circumstellar interaction similar to that displayed by SN 1993J in M 81 is taking place.

2025, arXiv (Cornell University)

We discuss the main ingredients necessary to build models of chemical evolution of spiral galaxies and in particular the Milky Way galaxy. These ingredients include: the star formation rate, the initial mass function, the stellar yields and the gas flows. Then we discuss models for the chemical evolution of galaxy disks and compare their predictions with the main observational constraints available for the Milky Way and other spirals. We conclude that it is very likely that the disk of our Galaxy and other spirals formed through an "inside-out" mechanism, where the central parts collapsed much faster than the external ones. This mechanism has important consequences for the appearance of galaxy disks as a function of redshift.

2025, Astronomy and Astrophysics

Context. The distribution of chemical abundances and their variation with time are important tools for understanding the chemical evolution of galaxies. In particular, the study of chemical evolution models can improve our understanding of the basic assumptions made when modelling our Galaxy and other spirals. Aims. We test a standard chemical evolution model for spiral disks in the Local Universe and study the influence of a threshold gas density and different efficiencies in the star formation rate (SFR) law on radial gradients of abundance, gas, and SFR. The model is then applied to specific galaxies. Methods. We adopt a one-infall chemical evolution model where the Galactic disk forms inside-out by means of infall of gas, and we test different thresholds and efficiencies in the SFR. The model is scaled to the disk properties of three Local Group galaxies (the Milky Way, M 31 and M 33) by varying its dependence on the star formation efficiency and the timescale for the infall of gas onto the disk. Results. Using this simple model, we are able to reproduce most of the observed constraints available in the literature for the studied galaxies. The radial oxygen abundance gradients and their time evolution are studied in detail. The present day abundance gradients are more sensitive to the threshold than to other parameters, while their temporal evolutions are more dependent on the chosen SFR efficiency. A variable efficiency along the galaxy radius can reproduce the present day gas distribution in the disk of spirals with prominent arms. The steepness in the distribution of stellar surface density differs from massive to lower mass disks, owing to the different star formation histories. Conclusions. The most massive disks seem to have evolved faster (i.e., with more efficient star formation) than the less massive ones, thus suggesting a downsizing in star formation for spirals. The threshold and the efficiency of star formation play a very important role in the chemical evolution of spiral disks. For instance, an efficiency varying with radius can be used to regulate the star formation. The oxygen abundance gradient can steepen or flatten in time depending on the choice of this parameter.

2025, Astronomy & Astrophysics

In a cosmological context dust has been always poorly understood. This is true also for the statistics of Gamma-Ray Bursts (GRBs). We therefore started a program to understand the role of dust both in GRBs and as function of z. This paper presents a composite model that considers a rather generic distribution of dust in a spiral galaxy and considers the effect of changing some of the parameters characterizing the dust grains, size in particular. We first simulated 500 GRBs distributed as the host galaxy mass distribution, using as a model the Milky Way. If we consider dust with the same properties as those we observe in the Milky Way, we find that due to absorption we miss ∼10% of the afterglows assuming we observe the event within 100 s-1 hr. In our second set of simulations we placed GRBs randomly inside giant molecular clouds, considering different kinds of dust inside and outside the host cloud and the effect of dust sublimation caused by the GRB inside the clouds. In this case absorption is mainly due to the host cloud and the physical properties of dust play a strong role. Computations from this model agree with the hypothesis of host galaxies with an extinction curve similar to that of the Small Magellanic Cloud, but the host cloud could be characterized also by dust with larger grains. Unfortunately, the present statistics lack significance, being based on incompatible observations, at different times from the burst and with different limiting magnitudes. To confirm our findings we need a set of homogeneous infrared observations. The use of forthcoming dedicated infrared telescopes, like REM, will provide a wealth of new afterglow observations.

2025, The Astronomical Journal

In recent years the number of worldwide 8∼10 m-class ground-based telescopes is continually increased, the 4 m-diameter or smaller telescopes have become the small and medium-sized telescopes. In order to obtain some noticeable scientific results by using these existing small and medium-sized telescopes, we have to consider very carefully what we can do, and what we can not. For this reason, the Time Allocation Committee of the 2.16 m telescope of the National Astronomical observatories of China (NAOC) has decided to support some key projects since 2013. The long-term project "Spectroscopic Observations of the Star Formation Regions in Nearby Galaxies" proposed by us is one of three key projects, it is supported by the committee with 30 dark/grey nights in each of three years. The primary goal of this project is to make the spectroscopic observations of the star formation regions along the directions parallel and perpendicular to the main-axes of 20 nearby galaxies with the NAO 2.16 m telescope and the Hectospec multi-fiber spectrograph on the 6.5 m MMT (Multiple Mirror Telescope) via the Telescope Access Program (TAP). With the spectra of a large sample of

2025, Publications of the Astronomical Society of Japan

The star formation rate in spiral galaxies is considered to be decreasing continuously with time in a time scale of 10 9 yr. The present star formation activity, on the other hand, occurs in molecular clouds with a time scale of 10 7 yr, and shows various degrees among galaxies. We make a new data set of 1681 nearby spiral galaxies from available databases and study the statistics of the present star formation activity. We analyze far-infrared and optical B-band surface brightnesses of the H II regions and the non-H II regions in M 31 and show that a far-infrared-to-optical B-band flux ratio, f FIR /f B , is a useful indicator of the present star formation activity of spiral galaxies. For the sample galaxies, we make the distribution diagram of log (f FIR /f B ) versus log L B for each morphological type. The distribution of f FIR /f B has a dispersion of one to two orders of magnitude even within the same morphological type of galaxies, implying that the star formation activities of spiral galaxies changes discontinuously in a short time scale. Analyzing the log (f FIR /f B ) versus log L B correlation, we suggest that the most active star formation in galaxies does not continue longer than 10 8 yr. We also construct a universal distribution histogram of log (f FIR /f B ) for each morphological type. The earlier-type spirals tend to show larger variation of the present star formation activity. We discuss the correlation between the present star formation activity and the structures and environments of galaxies. We suggest that the short-term variation occurs primarily due to internal processes which may change with the morphological type of galaxies.

2025, Publications of the Astronomical Society of Japan

We have obtained optical CCD spectroscopy along the major axes of 22 nearby spiral galaxies of Sb and Sc types in order to analyze their rotation curves. By subtracting the stellar continuum emission, we have obtained position-velocity (PV) diagrams of the Ha and [Nil] lines. We point out that the Ha line is often superposed by a broad stellar absorption feature (Balmer wing) in the nuclear regions, and, therefore, the [Nil] line is a better tracer of kinematics in the central few hundred parsec regions. By applying the envelope-tracing technique to the Ha and [Nil] PV diagrams, we have derived nucleus-to-disk rotation curves of the observed galaxies. The rotation curves rise steeply within the central few hundred parsecs, indicating a rapidly rotating nuclear disk and mass concentration near the nucleus.

2025, The Astronomical Journal

We examined the general characteristics of the Kiso Ultra-violet Excess Galaxies (KUGs). We present for the first time the quantitative expressions for the criteria of the KUGs; the boundary color separating the KUGs from the non-KUGs is (B -V ) T = 0.74 and the KUG degrees of UV strength are found to correlate with the mean (B -V ) T colors. We investigate the nature of the KUGs, a sample of blue galaxy population, and show that (1) about a half of the KUGs are spiral galaxies with Sb to Scd, (2) the KUGs are biased to late-type galaxies and include early-type galaxies with young star populations, and (3) the KUGs are preferably found among less luminous galaxies with L B < 10 10 L . The KUGs also contain the post-starburst galaxies, many of which are found among the blue galaxy population at intermediate redshifts. The analysis of the far-infrared data shows that a typical present-to-past star formation rate for a KUG is 0.4.

2025, Proceedings of the International Astronomical Union

We present first results from an HST/ACS imaging survey of stars and star clusters in five nearby spiral galaxies. This contribution concentrates on NGC 1313, a highly distorted late-type barred spiral. We compare the field star and cluster formation histories in our three ACS pointings for this galaxy. In one pointing, both the cluster and field star age distributions show clear evidence for a ramp-up in the star formation rate about 10 8 years ago.

2025, Astronomy and Astrophysics

Context. Star clusters are present in almost all types of galaxies. Here we investigate the star cluster population in the low-luminosity, unperturbed spiral galaxy NGC 45, which is located in the nearby Sculptor group. Both the old (globular) and young star-cluster populations are studied. Aims. Previous ground-based observations have suggested that NGC 45 has few if any "massive" young star clusters. We aim to study the population of lower-mass "open" star clusters and also identify old globular clusters that could not be distinguished from foreground stars in the ground-based data. Methods. Star clusters were identified using UBVI imaging from the Advanced Camera for Surveys (ACS) and the Wide Field Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope. From broad band colors and comparison with simple stellar population (SSP) models assuming a fixed metallicity, we derived the age, mass, and extinction. We also measured the radius for each star cluster candidate. Results. We identified 28 young star cluster candidates. While the exact values of age, mass, and extinction depend somewhat on the choice of SSP models, we find no young clusters with masses higher than a few 1000 M for any model choice. We derive the luminosity function of young star clusters and find a slope of α = -1.94 ± 0.28. We also identified 19 old globular clusters, which appear to have a mass distribution that is roughly consistent with what is observed in other globular cluster systems. Applying corrections for spatial incompleteness, we estimate a specific frequency of globular clusters of S N = 1.4-1.9, which is significantly higher than observed for other late-type galaxies (e.g. SMC, LMC, M 33). Most of these globular clusters appear to belong to a metal-poor population, although they coincide spatially with the location of the bulge of NGC 45.

2025

An accurate method to measure the abundance of high-redshift galaxies involves the observation of absorbers along the line of sight towards a background quasar. Here, we present abundance measurements of 13 z≥ 3 sub-damped Lyman α (sub-DLA) systems (quasar absorbers with H i column density in the range 19 3. These new data, combined with other sub-DLA measurements from the literature, confirm the stronger evolution of metallicity with redshift for sub-DLAs than for the classical damped Lyman α absorbers. In addition, these observations are used to compute for the first time, using photoionization modelling in a sample of sub-DLAs, the fraction of gas that is ionized. Based on these results, we calculate that sub-DLAs contribute no more than 6 per cent of the expected amount of metals at z∼ 2.5. We therefore conclude that, even if sub-DLAs are found to be more metal-rich than classical DLAs, their contribution is insufficient to solve the so-called ‘missing-metals' proble

2025, Revista Mexicana De Astronomia Y Astrofisica

2025, Astronomy and Astrophysics

The constituents of the cosmic IR background (CIB) are studied at its peak wavelengths (100 and 160 μm) by exploiting Herschel/PACS observations of the GOODS-N, Lockman Hole, and COSMOS fields in the PACS evolutionary probe (PEP) guaranteed-time survey. The GOODS-N data reach 3σ depths of ∼3.0 mJy at 100 μm and ∼5.7 mJy at 160 μm. At these levels, source densities are 40 and 18 beams/source, respectively, thus hitting the confusion limit at 160 μm. Differential number counts extend from a few mJy up to 100-200 mJy, and are approximated as a double power law, with the break lying between 5 and 10 mJy. The available ancillary information allows us to split number counts into redshift bins. At z ≤ 0.5 we isolate a class of luminous sources (L IR ∼ 10 11 L ), whose SEDs resemble late-spiral galaxies, peaking at ∼130 μm restframe and significantly colder than what is expected on the basis of pre-Herschel models. By integrating number counts over the whole covered flux range, we obtain a surface brightness of 6.36± 1.67 and 6.58± 1.62 [nW m -2 sr -1 ] at 100 and 160 μm, resolving ∼45% and ∼52% of the CIB, respectively. When stacking 24 μm sources, the inferred CIB lies within 1.1σ and 0.5σ from direct measurements in the two bands, and fractions increase to 50% and 75%. Most of this resolved CIB fraction was radiated at z ≤ 1.0, with 160 μm sources found at higher redshift than 100 μm ones.

2025, Astronomy and Astrophysics

Aims. We exploit the deepest existing far-infrared (FIR) data obtained so far by Herschel at 100 and 160 μm in the GOODS-N, as part of the PACS evolutionary probe (PEP) survey, to derive for the first time the evolution of the rest-frame 60-μm, 90-μm, and total IR luminosity functions (LFs) of galaxies and AGNs from z = 0 to unprecedented high redshifts (z ∼ 2-3). Methods. The PEP LFs were computed using the 1/V max method. The FIR sources were classified by means of a detailed broad-band SED-fitting analysis and spectral characterisation. Based on the best-fit model results, k-correction and total IR (8-1000 μm) luminosity were obtained for each source. LFs (monochromatic and total) were then derived for various IR populations separately in different redshift bins and compared to backward evolution model predictions. Results. We detect strong evolution in the LF to at least z ∼ 2. Objects with SEDs similar to local spiral galaxies are the major contributors to the star formation density (SFD) at z 0.3, then, as redshift increases, moderate SF galaxies -most likely containing a low-luminosity AGN -start dominating up to z 1.5. At z 1.5 the SFD is dominated by the contributions of starburst galaxies. In agreement with previous findings, the comoving IR LD derived from our data evolves approximately as (1 + z) 3.8±0.3 up to z ∼ 1, there being some evidence of flattening up to z ∼ 2.

2025

This paper presents an analytical solution to the geometry of large rotating sys-tems which reconciles the peculiar rotation profiles of distant galaxies with Einstein's principle of General Relativity. The resulting mathematical solution shows that large rotating systems are distorted in the space of a non-rotating observer into a spiral pat-tern with tangential velocities that behave in agreement with those observed in distant galaxies. This paper also demonstrates how the scale of the spiral structure of rotating systems can be used to determine its distance from the observer. The authors' pro-posed equations for the rotation profile and the distance measure are compared with the observed rotation profiles and Cepheid distance measurements of several galaxies with strong agreement. A formal error analysis is not included however the authors suggest a method for better qualifying the accuracy of the theorums.

2025

The morphology of a disk galaxy is closely linked to its kinematic state. This is because density wave features are likely made of spontaneously-formed modes which are allowed to arise in the galactic resonant cavity of a particular basic disk state. The pattern speed of a density wave is an important parameter that characterizes the wave and its associated resonances. Numerical simulations by various authors have enabled us to interpret some galaxies in terms of high or low pattern speeds. The potential-density phase-shift method for locating corotation radii is an effective new tool for utilizing galaxy morphology to determine the kinematic properties of galaxies. The dynamical mechanism underlying this association is also responsible for the secular evolution of galaxies. We describe recent results from the application of this new method to more than 150 galaxies in the Ohio State University Bright Galaxy Survey and other datasets.

2025, The Astrophysical Journal Supplement Series

The Spitzer Survey of Stellar Structure in Galaxies (S 4 G) is the largest available database of deep, homogeneous middle-infrared (mid-IR) images of galaxies of all types. The survey, which includes 2352 nearby galaxies, reveals galaxy morphology only minimally affected by interstellar extinction. This paper presents an atlas and classifications of S 4 G galaxies in the Comprehensive de Vaucouleurs revised Hubble-Sandage (CVRHS) system. The CVRHS system follows the precepts of classical de Vaucouleurs (1959) morphology, modified to include recognition of other features such as inner, outer, and nuclear lenses, nuclear rings, bars, and disks, spheroidal galaxies, X patterns and box/peanut structures, OLR subclass outer rings and pseudorings, bar ansae and barlenses, parallel sequence late-types, thick disks, and embedded disks in 3D early-type systems. We show that our CVRHS classifications are internally consistent, and that nearly half of the S 4 G sample consists of extreme late-type systems (mostly bulgeless, pure disk galaxies) in the range Scd-Im. The most common family classification for mid-IR types S0/a to Sc is SA while that for types Scd to Sm is SB. The bars in these two type domains are very different in mid-IR structure and morphology. This paper examines the bar, ring, and type classification fractions in the sample, and also includes several montages of images highlighting the various kinds of "stellar structures" seen in mid-IR galaxy morphology.

2025

We describe results from our study of a sample of spiral galaxies of a wide range of Hubble types on the basis of near-IR imaging obtained with INGRID on the WHT. We focus on the determination of bar torques, or bar strengths, from our... more

2025, The Astrophysical Journal

We have performed two-dimensional multicomponent decomposition of 144 local barred spiral galaxies using 3.6 μm images from the Spitzer Survey of Stellar Structure in Galaxies. Our model fit includes up to four components (bulge, disk, bar, and a point source) and, most importantly, takes into account disk breaks. We find that ignoring the disk break and using a single disk scale length in the model fit for Type II (down-bending) disk galaxies can lead to differences of 40% in the disk scale length, 10% in bulge-to-total luminosity ratio (B/T), and 25% in bar-to-total luminosity ratios. We find that for galaxies with B/T 0.1, the break radius to bar radius, r br /R bar , varies between 1 and 3, but as a function of B/T the ratio remains roughly constant. This suggests that in bulge-dominated galaxies the disk break is likely related to the outer Lindblad resonance of the bar and thus moves outward as the bar grows. For galaxies with small bulges, B/T < 0.1, r br /R bar spans a wide range from 1 to 6. This suggests that the mechanism that produces the break in these galaxies may be different from that in galaxies with more massive bulges. Consistent with previous studies, we conclude that disk breaks in galaxies with small bulges may originate from bar resonances that may be also coupled with the spiral arms, or be related to star formation thresholds.

2025, The Astrophysical Journal

Spiral arm properties of 46 galaxies in the Spitzer Survey of Stellar Structure in Galaxies (S 4 G) were measured at 3.6 μm, where extinction is small and the old stars dominate. The sample includes flocculent, multiple arm, and grand design types with a wide range of Hubble and bar types. We find that most optically flocculent galaxies are also flocculent in the mid-IR because of star formation uncorrelated with stellar density waves, whereas multiple arm and grand design galaxies have underlying stellar waves. Arm-interarm contrasts increase from flocculent to multiple arm to grand design galaxies and with later Hubble types. Structure can be traced further out in the disk than in previous surveys. Some spirals peak at mid-radius while others continuously rise or fall, depending on Hubble and bar type. We find evidence for regular and symmetric modulations of the arm strength in NGC 4321. Bars tend to be long, high amplitude, and flat-profiled in early-type spirals, with arm contrasts that decrease with radius beyond the end of the bar, and they tend to be short, low amplitude, and exponential-profiled in late Hubble types, with arm contrasts that are constant or increase with radius. Longer bars tend to have larger amplitudes and stronger arms.

2025, The Astronomical Journal

We have developed a new method for determining the corotation radii of density waves in disk galaxies, which makes use of the calculated radial distribution of an azimuthal phase shift between the potential and density wave patterns. The approach originated from improved theoretical understandings of the relation between the morphology and kinematics of galaxies, and on the dynamical interaction between density waves and the basic-state disk stars which results in the secular evolution of disk galaxies. In this paper, we present the rationales behind the method, and the first application of it to several representative barred and grand-design spiral galaxies, using near-infrared images to trace the mass distributions, as well as to calculate the potential distributions used in the phase shift calculations. We compare our results with those from other existing methods for locating the corotations, and show that the new method both confirms the previously-established trends of bar-length dependence on galaxy morphological types, as well as provides new insights into the possible extent of bars in disk galaxies. The method also facilitates the estimation of mass accretion/excretion rates due to bar and spiral density waves, providing an alternative way of quantifying the importance of these features in disk galaxies. A preliminary analysis of a larger sample shows that the phase shift method is likely to be a generally-applicable, accurate, and essentially model-independent method for determining the pattern speeds and corotation radii of single or nested density wave patterns in galaxies. Other implications of the results of this work include that most of the nearby bright disk galaxies appear to possess quasi-stationary spiral modes; that these density wave modes as well as the associated basic-states of the galactic disks slowly transform over the time span of a Hubble time due to a collective dissipation process directly related to the presence of the phase shift between the potential and density patterns; and that self-consistent N-particle systems contain physics not revealed by the passive orbit analysis approaches.

2025, The Astronomical Journal

This paper reports on a near-infrared survey of early-type galaxies designed to provide information on bar strengths, bulges, disks, and bar parameters in a statistically well-defined sample of S0-Sa galaxies. Early-type galaxies have the advantage that their bars are relatively free of the effects of dust, star formation, and spiral structure that complicate bar studies in later type galaxies. We describe the survey and present results on detailed analysis of the relative Fourier intensity amplitudes of bars in 26 early-type galaxies. We also evaluate the symmetry assumption of these amplitudes with radius, used recently for bar-spiral separation in later-type galaxies. The results show a wide variety of radial Fourier profiles of bars, ranging from simple symmetric profiles that can be represented in terms of a single gaussian component, to both symmetric and asymmetric profiles that can be represented by two overlapping gaussian components. More complicated profiles than these are also found, often due to multiple bar-like features including extended ovals or lenses. Based on the gravitational bar torque indicator Q b , double-gaussian bars are stronger on average than single-gaussian bars, at least for our small sample. We show that published numerical simulations where the bar transfers a large amount of angular momentum to the halo can account for many of the observed profiles. The range of possibilities encountered in models seems well-represented in the observed systems.

2025, Astrophysics and Space Science

We investigate the variation of bar strength with central velocity dispersion in a sample of barred spiral galaxies. The bar strength is characterized by Q g , the maximal tangential perturbation associated with the bar, normalized by the mean axisymmetric force. It is derived from the galaxy potentials which are obtained using near-infrared images of the galaxies. However, Q g is sensitive to bulge mass. Hence we also estimated bar strengths from the relative Fourier intensity amplitude (A 2 ) of bars in near-infrared images. The central velocity dispersions were obtained from integral field spectroscopy observations of the velocity fields in the centers of these galaxies; it was normalized by the rotation curve amplitude obtained from HI line width for each galaxy. We found a correlation between bar strengths (both Q g and A 2 ) and the normalized central velocity dispersions in our sample. This suggests that bars weaken as their central components become kinematically hotter. This may have important implications for the secular evolution of barred galaxies.

2025, The Astrophysical Journal Supplement Series

The potential-density phase-shift method is an effective new tool for investigating the structure and evolution of galaxies. In this paper, we apply the method to 153 galaxies in the Ohio State University Bright Galaxy Survey (OS-UBGS) to study the general relationship between pattern corotation radii and the morphology of spiral galaxies. The analysis is based on near-infrared H-band images that have been deprojected and decomposed assuming a spherical bulge. We find that multiple pattern speeds are common in disk galaxies. By selecting those corotation radii close to or slightly larger than the bar radius as being the bar corotation (CR) radius, we find that the average and standard deviation of the ratio R = r(CR)/r(bar), is 1.20±0.52 for 101 galaxies having well-defined bars. There is an indication that this ratio depends weakly on galaxy type in the sense that the average ranges from 1.03±0.37 for 65 galaxies of type Sbc and earlier, to 1.50±0.63 for 36 galaxies of type Sc and later. Our bar corotation radii are on average smaller than those estimated from single-pattern-speed numerical simulations, most likely because these simulations tend to find the pattern speed which generates a density response in the gas that best matches the morphology of the outer spiral structure. Although we find CR radii in most of the sample galaxies that satisfy conventional ideas about the extent of bars, we also consider the alternative interpretation that in many cases the bar CR is actually inside the bar and that the bar ends close to its outer Lindblad resonance instead of its CR. These "super-fast" bars are the most controversial finding from our study. We see evidence in the phase-shift distributions for ongoing decoupling of patterns, which hints at the formation pathways of nested patterns, and which in turn further hints at the longevity of the density wave patterns in galaxies. We also examine how uncertainties in the orientation parameters of galaxies and in

2025

Galaxy morphology has many structures that are suggestive of various processes or stages of secular evolution. Internal perturbations such as bars can drive secular evolution through gravity torques that move gas into the central regions and build up a flattened, disk-like central bulge, or which may convert an open spiral pseudoring into a more closed ring. Interaction between individual components of a galaxy, such as between a bar and a dark halo, a bar and a central mass concentration, or between a perturbation and the basic state of a stellar disk, can also drive secular transformations. In this series of lectures, I review many aspects of galaxy morphology with a view to delineating some of the possible evolutionary pathways between different galaxy types.

2025

This hypothesis proposes that planetary cores are not merely byproducts of accretion, but rather active gravitational structures that follow principles similar to black holes-though at inverse scales. Through an adaptation of the Schwarzschild radius applied in reverse and new interpretations of internal gravitational dynamics, it is posited that the formation of the planetary core is the first "functional organ" that sustains gravity and organizes surrounding matter.

2025

2025, AAS

We present Spitzer Space Telescope IRAC photometry of the Local Group dwarf irregular galaxy IC 1613. We compare our 3.6, 4.5, 5.8, and 8.0 µm photometry with broadband optical photometry and find that the optical data do not detect 43% and misidentify an additional 11% of the total AGB population, likely because of extinction caused by circumstellar material. Further, we find that a narrowband optical carbon star study of IC 1613 detects 50% of the total AGB population and only considers 18% of this population in calculating the carbon to M-type AGB ratio. We derive an integrated mass-loss rate from the AGB stars of 0.2-1.0×10 -3 M ⊙ yr -1 and find that the distribution of bolometric luminosities and mass-loss rates are consistent with those for other nearby metal-poor galaxies. Both the optical completeness fractions and mass-loss rates in IC 1613 are very similar to those in the Local Group dwarf irregular, WLM, which is expected given their similar characteristics and evolutionary histories.

2025

présentée pour obtenir le grade de Docteur de l’Université de Provence

2025, arXiv: Astrophysics of Galaxies

The nearby S0 galaxy IC 5181 is studied to address the origin of the ionized gas component that orbits the galaxy on polar orbit. We perform detailed photometric and spectroscopic observations measuring the surface brightness distribution of the stars (I-band), ionized gas of IC 5181 (H-alpha narrow band), the ionized-gas and stellar kinematics along both the major and minor axis, and the corresponding line strengths of the Lick indices. We conclude that the galaxy hosts a geometrically and kinematically decoupled component of ionized gas. It is elongated along the galaxy minor axis and in orthogonal rotation with respect to the galaxy disk. The result is suggesting that the gas component is not related to the stars having an external origin. The gas was accreted by IC 5181 on polar orbits from the surrounding environment.

2025, Astronomy & Astrophysics

We present the results of narrow-band Halpha +[N riptsize II] imaging of the early-type spiral NGC 3593 in combination with a study of the flux radial profiles of the [N riptsize II] (lambda lambda 654.80, 658.34 nm), Halpha , and [S riptsize II] (lambda lambda 671.65, 673.08 nm) emission lines along its major axis. The galaxy is known to contain

2025

We present a comparison between ionized gas and stellar kinematics for a sample of 5 early-to-intermediate disk galaxies. We measured the major axis V and velocity dispersion radial profiles for both gas and stars, and the h_3 and h_4 radial profiles of the stars. We also derived from the R-band surface photometry of each galaxy the light contribution of their

2025, The Astrophysical Journal

We report the discovery of two counterrotating stellar disks in the early-type spiral galaxy NGC 3593. The major axis kinematics shows the presence of two dynamically cold counterrotating components. The surface brightness profile is well reproduced by the sum of the contributions of two exponential disks of different scale lengths (r 1 ϭ 40Љ; r 2 ϭ 10Љ) and different central surface brightnesses ( r,1 ϭ 19.9; r,2 ϭ 18.5 mag arcsec Ϫ2 ). The v and radial profiles are easily reproduced by the means of a kinematical model adopting the above photometric parameters. An ionized gas disk is present. It corotates with the smaller scale length and less massive (M 2 ϭ 2.7 ϫ 10 9 M J ) disk, and counterrotates with the larger and more massive (M 1 ϭ 1.2 ϫ 10 10 M J ) one. We conclude that the smaller stellar disk is the result of a slow adiabatic acquisition of a conspicuous amount of counterrotating gas (M infall 1 4.3 ϫ 10 9 M J ) by the preexisting galaxy, originally constituted mainly by a gas-free stellar disk (disk 1). The counterrotating gas settled into the equatorial plane and then formed the inner stellar disk (disk 2).

2025

We measured a remarkable gas velocity gradient along the minor axis of a number of early-type spiral galaxies. This phenomenon suggests the presence of a kinematically-decoupled component in orthogonal rotation with respect to the galaxy disk which we named inner polar disk. If this is the case a second event has taken place in the history of the galaxy. Alternatively the gas velocity gradient is the result of non-circular motions induced by the potential of a triaxial bulge.

2025, Arxiv preprint astro-ph/ …

2025

We measured the velocity curve and the velocity dispersion profile of the ionized gas along the major axis of the edge-on galaxy UGC 10205. The observed kinematics extends up to about 40 from the nucleus. In the inner ±13 of this earlytype spiral three kinematically distinct gaseous components are present. We disentangle a fast-rotating and a slow-rotating component. They give to the UGC 10205 velocity curve a "figure-ofeight" appearance. A third velocity component is also detected on the southeast side of the galaxy. Possibly it is produced by gas in non-circular motions.

2025

In the Kha theory the force of gravity on particles is due to the pressure from cosmic neutrinos. I explain how the black holes were formed by the enormous pressure from the neutrinos in the original soup. In our contemporary universe the pressure from the cosmic neutrinos is much less, but the cosmic neutrinos are still responsible for the gravitation. If the neutrinos were coming from all directions the total force on the earth
would vanish and the resulting force on the earth would be zero. However the sun afford shade from part of the external universe.

2025, International Journal of Modern Physics D