Early Spirals Research Articles

The Halo Mass–Temperature Relation for Clusters, Groups, and Galaxies

The halo mass–temperature (M–T) relation for a sample of 216 galaxy clusters, groups, and individual galaxies observed by the Chandra X-ray Observatory is presented. Using accurate spectral measurements of their hot atmospheres, we derive the M–T relation for systems with temperatures ranging between 0.4 and 15.0 keV. We measure the total masses of the clusters, groups, and galaxies at radius R 2500, finding that the M 2500 ∝ T α relation follows a power law with α = 1.65 ± 0.06. Our relation agrees with recent lensing studies of the M–T relation at R 200 and is consistent with self-similar theoretical predictions and recent simulations. This agreement indicates that the M–T relation is weakly affected by nongravitational heating processes. Using lensing masses within R 200 we find M 200–T follows a power law with a slope of 1.61 ± 0.19, consistent with the M 2500–T relation. No evidence for a break or slope change is found in either relation. Potential biases associated with sample selection, evolution, and the assumption of hydrostatic equilibrium that may affect the scaling are examined. No significant impacts attributable to these biases are found. Non-cool-core clusters and early spirals produce higher scatter in the M–T relation than cool-core clusters and elliptical galaxies.

Beyond the hubble sequence – exploring galaxy morphology with unsupervised machine learning

ABSTRACT We explore unsupervised machine learning for galaxy morphology analyses using a combination of feature extraction with a vector-quantized variational autoencoder (VQ-VAE) and hierarchical clustering (HC). We propose a new methodology that includes: (1) consideration of the clustering performance simultaneously when learning features from images; (2) allowing for various distance thresholds within the HC algorithm; (3) using the galaxy orientation to determine the number of clusters. This set-up provides 27 clusters created with this unsupervised learning that we show are well separated based on galaxy shape and structure (e.g. Sérsic index, concentration, asymmetry, Gini coefficient). These resulting clusters also correlate well with physical properties such as the colour–magnitude diagram, and span the range of scaling relations such as mass versus size amongst the different machine-defined clusters. When we merge these multiple clusters into two large preliminary clusters to provide a binary classification, an accuracy of $\sim 87{{\ \rm per\ cent}}$ is reached using an imbalanced data set, matching real galaxy distributions, which includes 22.7 per cent early-type galaxies and 77.3 per cent late-type galaxies. Comparing the given clusters with classic Hubble types (ellipticals, lenticulars, early spirals, late spirals, and irregulars), we show that there is an intrinsic vagueness in visual classification systems, in particular galaxies with transitional features such as lenticulars and early spirals. Based on this, the main result in this work is not how well our unsupervised method matches visual classifications and physical properties, but that the method provides an independent classification that may be more physically meaningful than any visually based ones.

Origins of Molecular Clouds in Early-type Galaxies

Abstract We analyze Chandra observations of the hot atmospheres of 40 early spiral and elliptical galaxies. Using new temperature, density, cooling time, and mass profiles, we explore relationships between their hot atmospheres and cold molecular gas. Molecular gas mass correlates with atmospheric gas mass and density over four decades from central galaxies in clusters to normal giant ellipticals and early spirals. The mass and density relations follow power laws: and , respectively, at 10 kpc. The ratio of molecular gas to atmospheric gas within a 10 kpc radius lies between 3% and 10% for early-type galaxies and between 3% and 50% for central galaxies in clusters. Early-type galaxies have detectable levels of molecular gas when their atmospheric cooling times fall below ∼1 Gyr at a radius of 10 kpc. A similar trend is found in central cluster galaxies. We find no relationship between the ratio of the cooling time to free-fall time, t c/t ff, and the presence or absence of molecular clouds in early-type galaxies. The data are consistent with much of the molecular gas in early-type galaxies having condensed from their hot atmospheres.

Spatially-resolved star formation histories of CALIFA galaxies

This paper presents the spatially resolved star formation history (SFH) of nearby galaxies with the aim of furthering our understanding of the different processes involved in the formation and evolution of galaxies. To this end, we apply the fossil record method of stellar population synthesis to a rich and diverse data set of 436 galaxies observed with integral field spectroscopy in the CALIFA survey. The sample covers a wide range of Hubble types, with stellar masses ranging fromM⋆~ 109to 7 × 1011M⊙. Spectral synthesis techniques are applied to the datacubes to retrieve the spatially resolved time evolution of the star formation rate (SFR), its intensity (ΣSFR), and other descriptors of the 2D SFH in seven bins of galaxy morphology (E, S0, Sa, Sb, Sbc, Sc, and Sd) and five bins of stellar mass. Our main results are that (a) galaxies form very fast independently of their current stellar mass, with the peak of star formation at high redshift (z> 2). Subsequent star formation is driven byM⋆and morphology, with less massive and later type spirals showing more prolonged periods of star formation. (b) At any epoch in the past, the SFR is proportional toM⋆, with most massive galaxies having the highest absolute (but lowest specific) SFRs. (c) While today, the ΣSFRis similar for all spirals and significantly lower in early-type galaxies (ETG), in the past, the ΣSFRscales well with morphology. The central regions of today’s ETGs are where the ΣSFRreached the highest values (> 103M⊙Gyr-1pc-2), similar to those measured in high-redshift star-forming galaxies. (d) The evolution of ΣSFRin Sbc systems matches that of models for Milky Way-like galaxies, suggesting that the formation of a thick disk may be a common phase in spirals at early epochs. (e) The SFR and ΣSFRin outer regions of E and S0 galaxies show that they have undergone an extended phase of growth in mass betweenz= 2 and 0.4. The mass assembled in this phase is in agreement with the two-phase scenario proposed for the formation of ETGs. (f) Evidence of an early and fast quenching is found only in the most massive (M⋆> 2 × 1011M⊙) E galaxies of the sample, but not in spirals of similar mass, suggesting that halo quenching is not the main mechanism for the shut down of star formation in galaxies. Less massive E and disk galaxies show more extended SFHs and a slow quenching. (g) Evidence of fast quenching is also found in the nuclei of ETG and early spirals, with SFR and ΣSFRindicating that they can be the relic of the “red nuggets” detected at high redshift.

A NEW PRIABONIANHETEROSTEGINAFROM THE EASTERN TETHYS (SULAIMAN FOLD BELT, WEST PAKISTAN): IMPLICATIONS FOR THE DEVELOPMENT OF EASTERN TETHYAN HETEROSTEGINES AND THEIR PALEOBIOGEOGRAPHY

The stratigraphic utility of Eocene Heterostegina in the Western Tethys prompts an interest in the Eastern Tethyan domain, where virtually no information exists on this group. The classic Eocene sections, Zinda Pir and Rakhi Nala, in West Pakistan offer a unique opportunity to fill this information gap. The genus here is confined only to the upper part of the Drazinda Formation (‘ Pellatispira beds’ of the obsolete Kirthar series) associated with Pellatispira , Silvestriella , reticulate Nummulites , rare orthophragminids and other less significant larger benthic foraminifera. Heterostegina specimens are characterised by notably small, nearly flat to flat tests with fine granulation over the test surface, a small proloculus and tight early spirals. The early operculinid chambers, few in number, are followed by the heterosteginid stage consisting of rectangular chamberlets, developed only in the median part of the test, but not in alar prolongations. The latter are remarkably wide and extend to the umbilical part of the test. A combination of these features permits their differentiation from the Western Tethyan and Pacific Eocene Heterostegina , also demonstrated morphometrically, and a new species, H. indusensis n. sp., is erected. Our data favor the polyphyletic origin for the Eocene heterostegines in the Tethys and do not support a previous hypothesis that the genus was confined to the high-latitutes in Priabonian times.

Supernovae and their host galaxies – II. The relative frequencies of supernovae types in spirals

We present an analysis of the relative frequencies of different supernova (SN) types in spirals with various morphologies and in barred or unbarred galaxies. We use a well-defined and homogeneous sample of spiral host galaxies of 692 SNe from the Sloan Digital Sky Survey in different stages of galaxy-galaxy interaction and activity classes of nucleus. We propose that the underlying mechanisms shaping the number ratios of SNe types can be interpreted within the framework of interaction-induced star formation, in addition to the known relations between morphologies and stellar populations. We find a strong trend in behaviour of the NIa/NCC ratio depending on host morphology, such that early spirals include more Type Ia SNe. The NIbc/NII ratio is higher in a broad bin of early-type hosts. The NIa/NCC ratio is nearly constant when changing from normal, perturbed to interacting galaxies, then declines in merging galaxies, whereas it jumps to the highest value in post-merging/remnant galaxies. In contrast, the NIbc/NII ratio jumps to the highest value in merging galaxies and slightly declines in post-merging/remnant subsample. The interpretation is that the star formation rates and morphologies of galaxies, which are strongly affected in the final stages of interaction, have an impact on the number ratios of SNe types. The NIa/NCC (NIbc/NII) ratio increases (decreases) from star-forming to active galactic nuclei (AGN) classes of galaxies. These variations are consistent with the scenario of an interaction-triggered starburst evolving into AGN during the later stages of interaction, accompanied with the change of star formation and transformation of the galaxy morphology into an earlier type.

Inclination‐Independent Galaxy Classification

We present a new method to classify galaxies from large surveys like the Sloan Digital Sky Survey using inclination-corrected concentration, inclination-corrected location on the color-magnitude diagram, and apparent axis ratio. Explicitly accounting for inclination tightens the distribution of each of these parameters and enables simple boundaries to be drawn that delineate three different galaxy populations: Early-type galaxies, which are red, highly concentrated, and round; Late-type galaxies, which are blue, have low concentrations, and are disk dominated; and Intermediate-type galaxies, which are red, have intermediate concentrations, and have disks. We have validated our method by comparing to visual classifications of high-quality imaging data from the Millennium Galaxy Catalogue. The inclination correction is crucial to unveiling the previously unrecognized Intermediate class. Intermediate-type galaxies, roughly corresponding to lenticulars and early spirals, lie on the red sequence. The red sequence is therefore composed of two distinct morphological types, suggesting that there are two distinct mechanisms for transiting to the red sequence. We propose that Intermediate-type galaxies are those that have lost their cold gas via strangulation, while Early-type galaxies are those that have experienced a major merger that either consumed their cold gas, or whose merger progenitors were already devoid of cold gas (the ``dry merger'' scenario).

A new sample of bright galaxy pairs in UZC

We present a new sample of bright galaxy pairs extracted applying an objective selection code to UZC catalog.The sample is volume limited to M$_{zw}$ = -18.9 +5 log ${\it h}$ and contains 89 galaxy pairs.We analyze the kinematical, morphological and photometrical properties of galaxies belonging to this sample. We show that velocity separation, $| \Delta v_{r} |$, between pair members is significantly lower in spiral type (S+S) pairs than in early-type (E+E) and mixed (E+S) pairs.This indicates that truly isolated galaxy pairs are more likely to be found among S+S pairs. We show that ellipticals are rare and underluminous in B and that late spirals (T $\ge$ 4) are overluminous. We confirm that the formation of bright ellipticals is a phenomenon linked to group/cluster environment, while galaxy-galaxy interaction may enhance blue luminosity of disk galaxies through SF phenomena. This last statement is supported by the presence of strong FIR emission from early spirals in this sample and by the high frequency of AGN/SB phenomenon, revealed mainly in pairs of low relative radial velocity separation and showing signs of interaction.

Nuclear Activity in UZC Compact Groups

AbstractWe have analyzed the level and type of nuclear activity in 720 galaxies belonging to a large complete sample of Compact Groups (UZC-CGs). We have found that most (67%) galaxies show emission lines and that the most frequent (43%) nuclear activity is AGN. AGNs are mainly hosted in bright early type galaxies and early spirals, at variance with HII which reside in late spirals of lower luminosity. CGs which have a dominant content of AGNs and TOs have larger σv and lower Rp than CGs dominated by HII.

The ESO nearby Abell cluster survey

We study the morphology-radius and morphology-density relations for a sample of about 850 galaxies (with ) in 23 clusters from the ENACS (ESO Nearby Abell Cluster Survey). On the basis of their radial distributions we must distinguish: (i) the brightest ellipticals (with ); (ii) the late spirals, and (iii) the ensemble of the less bright ellipticals, the S0 galaxies and the early spirals, which have indistinguishable distributions of projected radial distance R. The brightest ellipticals are most centrally concentrated, while the late spirals are almost absent from the central regions; the radial distribution of the other galaxy classes is intermediate. The previously found radial segregation of the ellipticals thus appears to be due to the brightest ellipticals only, while that of the spirals is due to the late spirals only. The morphology-density (MD-) relation was derived with two measures of projected density: one using the 10 nearest neighbours () and another using only the nearest neighbour (). In the MD-relation, only the classes of early- and late-type galaxies show a significant difference, but the different galaxy types within those classes are indistinguishable. However, this result is affected by significant cross-talk from the morphology-radius (or MR-) relation, as is strongly correlated with R. appears much less correlated with R and therefore the crosstalk from the MR-relation is much smaller. As a result, the normal “ellipticals” (with ), the S0 galaxies and the early spirals do have different -distributions. On average, the “normal” ellipticals populate environments with higher projected density than do the S0 galaxies while the early spirals populate even less dense environments. We conclude that the segregation of the brightest ellipticals and the late spirals is driven primarily by global factors, while the segregation between “normal” ellipticals, S0 galaxies and early spirals is driven mostly by local factors. We discuss briefly the implications of these results in terms of scenarios for formation and transformation of galaxies in clusters.

The ESO nearby Abell cluster survey

We determine the morphological types of 2295 galaxies from the ESO Nearby Abell Cluster Survey (ENACS) from CCD images obtained with the Dutch telescope on La Silla. A comparison with morphological types from the literature for 450 of our galaxies shows that the reliability of our classification is quite comparable to that of other classifiers. We recalibrate the ENACS spectral classification with the new morphological types, and find that early- and late-type galaxies can be distinguished from their spectra with 83% reliability. Ellipticals and S0 galaxies can hardly be distinguished on the basis of their spectra, but late spirals can be classified from the spectrum alone with more than 70% reliability. We derive pseudo-colors and linestrengths from the ENACS spectra for the galaxies of different morphological types. We consider the bright () and faint () subsets of the galaxies without emission lines (non-ELG) separately. We find a strong and significant correlation between the average color and the average strength of the metal absorption lines. The average metallicity decreases and the average color gets bluer towards later Hubble type. Also, the faint galaxies in each morphological class are bluer and less metal-rich than their brighter counterparts, which extends the well-established color-magnitude relation of early-type galaxies to (late) spirals. In view of these very strong global trends, the colors and metallicities of faint S0 galaxies and bright early spirals are remarkably similar. The bright early spirals may, on average, have somewhat stronger Hδ absorption than the other galaxies, which could be due to recent starformation. The galaxies with emission lines (ELG) have a bluer spectral continuum than the non-ELG, and the amount of blueing hardly depends on morphological type. The fraction of ELG depends strongly on morphological type (varying from % for ellipticals to % for late spirals), but for each of the morphological types it varies very little with projected distance from the cluster center.

The Intrinsic Shape of Spiral Galaxies in the 2MASS Large Galaxy Atlas

The apparent shapes of spiral galaxies in the 2-Micron All Sky Survey Large Galaxy Atlas are used to constrain the intrinsic shape of their disks. When the distribution of apparent axis ratios is estimated using a nonparametric kernel method, the shape distribution is inconsistent with axisymmetry at the 90% confidence level in the B band and at the 99% confidence level in the K band. If spirals are subdivided by Hubble type, the late-type spirals (Sc and later) are consistent with axisymmetry, while the earlier spirals are strongly inconsistent with axisymmetry. The distribution of disk ellipticity can be fitted adequately with either a Gaussian or a lognormal distribution. The best fits for the late spirals imply a median ellipticity of epsilon = 0.07 in the B band and epsilon = 0.02 in the K band. For the earlier spirals, the best fits imply a median ellipticity of epsilon = 0.18 in the B band and epsilon = 0.30 in the K band. The observed scatter in the Tully-Fisher relation, for both late and early spirals, is consistent with the disk ellipticity measured in the B band. This indicates that excluding spirals of Hubble type earlier than Sc will reduce the intrinsic scatter in the Tully-Fisher relation used as a distance indicator.

The ESO Nearby Abell Cluster Survey

We study the orbits of the various types of galaxies observed in the ESO Nearby Abell Cluster Survey. We combine the observed kinematics and projected distributions of galaxies of various types with an estimate of the mass density profile of the ensemble cluster to derive velocity-anisotropy profiles. Galaxies within and outside substructures are considered separately. Among the galaxies outside substructures we distinguish four classes, on the basis of their projected phase-space distributions. These classes are: the brightest ellipticals (with ), the other ellipticals together with the S0's, the early-type spirals (Sa–Sb), and the late-type spirals and irregulars (Sbc-Irr) together with the emission-line galaxies (except those of early morphology). The mass profile was determined from the distribution and kinematics of the early-type (i.e. elliptical and S0) galaxies outside substructures; the latter were assumed to be on isotropic orbits, which is supported by the shape of their velocity distribution. The projected distribution and kinematics of the galaxies of other types are used to search for equilibrium solutions in the gravitational potential derived from the early-type galaxies. We apply the method described by Binney & Mamon as implemented by Solanes & Salvador-Solé to derive, to our knowledge for the first time, the velocity anisotropy profiles of all galaxy classes individually (except, of course, the early-type class). We check the validity of the solutions for , where and are the mean squared components of the radial and tangential velocity, respectively, by comparing the observed and predicted velocity-dispersion profiles. For the brightest ellipticals we are not able to construct equilibrium solutions. This is most likely the result of the formation history and the special location of these galaxies at the centres of their clusters. For both the early and the late spirals, as well as for the galaxies in substructures, the data allow equilibrium solutions. The data for the early spirals are consistent with isotropic orbits (), although there is an apparent radial anisotropy at . For the late spirals an equilibrium solution with isotropic orbits is rejected by the data at the >99% confidence level. While within , increases linearly with radius to a value 1.8 at . Taken at face value, the data for the galaxies in substructures indicate that isotropic solutions are not acceptable, and tangential orbits are indicated. Even though the details of the tangential anisotropy remain to be determined, the general conclusion appears robust. We briefly discuss the possible implications of these velocity-anisotropy profiles for current ideas of the evolution and transformation of galaxies in clusters.

Properties of isolated disk galaxies

We present a new sample of northern isolated galaxies, which are defined by the physical criterion that they were not affected by other galaxies in their evolution during the last few Gyr. To find them we used the logarithmic ratio, f , between inner and tidal forces acting upon the candidate galaxy by a possible perturber. The analysis of the distribution of the f -values for the galaxies in the Coma cluster lead us to adopt the criterion f ≤− 4.5 for isolated galaxies. The candidates were chosen from the CfA catalog of galaxies within the volume defined bycz ≤ 5000 km s −1 , galactic latitude higher than 40 ◦ and declination ≥−2.5 ◦ . The selection of the sample, based on redshift values (when available), magnitudes and sizes of the candidate galaxies and possible perturbers present in the same field is discussed. The final list of selected isolated galaxies includes 203 objects from the initial 1706. The list contains only truly isolated galaxies in the sense defined, but it is by no means complete, since all the galaxies with possible companions under the f -criterion but with unknown redshift were discarded. We also selected a sample of perturbed galaxies comprised of all the disk galaxies from the initial list with companions (with known redshift) satisfying f ≥− 2a nd∆(cz) ≤ 500 km s −1 ; a total of 130 objects. The statistical comparison of both samples shows significant differences in morphology, sizes, masses, luminosities and color indices. Confirming previous results, we found that late spiral, Sc-type galaxies are, in particular, more frequent among isolated galaxies, whereas Lenticular galaxies are more abundant among perturbed galaxies. Isolated systems appear to be smaller, less luminous and bluer than interacting objects. We also found that bars are twice as frequent among perturbed galaxies compared to isolated galaxies, in particular for early Spirals and Lenticulars. The perturbed galaxies have higher LFIR/LB and Mmol/LB ratios, but the atomic gas content is similar for the two samples. The analysis of the luminosity-size and mass-luminosity relations shows similar trends for both families, the main difference being the almost total absence of big, bright and massive galaxies among the family of isolated systems, together with the almost total absence of small, faint and low mass galaxies among the perturbed systems. All these aspects indicate that the evolution induced by interactions with neighbors would proceed from late, small, faint and low mass Spirals to earlier, bigger, more luminous and more massive spiral and lenticular galaxies, producing at the same time a larger fraction of barred galaxies but preserving the same relations between global parameters. The properties we found for our sample of isolated galaxies appear similar to those of high redshift galaxies, suggesting that the present-day isolated galaxies could be quietly evolved, unused building blocks surviving in low density environments.

Galaxies in present-day clusters: evolutionary constraints from their distributions and kinematics

We discuss evidence in local, present-day clusters of galaxies (from the ENACS survey) about the way in which those clusters have evolved and about the evolutionary relationships between the galaxies of different morphological types in them. This evidence is complementary to that obtained from the study of clusters at intermediate and high redshifts. We argue that the spatial distribution and the kinematics of the various types of galaxies in and outside substructures support the following picture. The ELLIPTICAL AND S0 GALAXIES have been around for a long time and have obtained an isotropic velocity distribution. The spatial distribution and kinematics of the EARLY SPIRALS are consistent with the idea that many of their kind have transformed into an S0, but that they have survived, most likely because of their velocities. The distribution and kinematics of the LATE SPIRALS are consistent with a picture in which they have been accreted fairly recently. They have mildly radial orbits and hardly populate the central regions, most likely because they suffer tidal disruption. Finally, the distribution and kinematics of the GALAXIES IN SUBSTRUCTURES, when taken at face value, imply tangential velocity anisotropy for these galaxies, but this result may be (partly) due to the procedure by which these galaxies are selected. A first attempt to take the effects of selection into account shows that isotropic (or even mildly radial) orbits of subcluster galaxies cannot be excluded.

The properties of the galaxies in the ENACS clusters, and the relation between spirals and S0 galaxies

We discuss the properties of the galaxies in about 60 rich, nearby clusters, using kinematic data from the ESO Nearby Abell Cluster Survey, combined with new imaging data. The images were used to classify the galaxies, and to recalibrate the galaxy types derived from the ENACS spectra; this yields galaxy-type estimates for about 4800 galaxies. For about 1200 galaxies, a bulge/disk decomposition could be made, which yields sizes and luminosities of bulges and disks. From the projected radial distances and relative l.o.s.-velocities we derived the galaxy ensembles with significantly different phase-space distributions. We find that galaxies in and outside substructure must be distinguished. The morphological composition of the substructures appears to vary with projected radius. Outside substructures, 4 galaxy ensembles must be defined: viz. the brighest Es, the other early-type galaxies, the early spirals (Sa-Sb), and the late spirals (including the emission-line galaxies). We also study the morphology-density relation, and we find that the segregation of the late spirals is driven mostly by global factors, while the segregation of Es, S0s and early spirals is driven mostly by local density. The properties of early spirals and S0s support the picture in which early spirals transform into S0s, while the properties of the late spirals do not support such a relation.

Rotation curves and metallicity gradients from HII regions in spiral galaxies

In this paper we study long slit spectra in the region of H$\alpha$ emission line of a sample of 111 spiral galaxies with recognizable and well defined spiral morphology and with a well determined environmental status, ranging from isolation to non-disruptive interaction with satellites or companions. The form and properties of the rotation curves are considered as a function of the isolation degree, morphological type and luminosity. The line ratios are used to estimate the metallicity of all the detected HII regions, thus producing a composite metallicity profile for different types of spirals. We have found that isolated galaxies tend to be of later types and lower luminosity than the interacting galaxies. The outer parts of the rotation curves of isolated galaxies tend to be flatter than in interacting galaxies, but they show similar relations between global parameters. The scatter of the Tully-Fisher relation defined by isolated galaxies is significantly lower than that of interacting galaxies. The [NII]/H$\alpha$ ratios, used as metallicity indicator, show a clear trend between Z and morphological type, t, with earlier spirals showing larger ratios; this trend is tighter when instead of t the gradient of the inner rotation curve, G, is used; no trend is found with the interaction status. The Z-gradient of the disks depends on the type, being almost flat for early spirals, and increasing for later types. The [NII]/H$\alpha$ ratios measured for disk HII regions of interacting galaxies are higher than for normal/isolated objects, even if all the galaxy families present similar distributions of H$\alpha$ Equivalent Width.

The percentage of stellar light re-radiated by dust in late-type Virgo Cluster galaxies

We show that the mean percentage of stellar light re-radiated by dust is ∼30 per cent for the Virgo Cluster late-spirals measured with ISOPHOT by Tuffs et al. A strong dependence of this ratio with morphological type was found, ranging from typical values of ∼15 per cent for early spirals to up to ∼50 per cent for some late spirals. The extreme BCDs can have even higher percentages of their bolometric output re-radiated in the thermal infrared. Luminosity correction factors for the cold dust component are given for general use in converting far-infrared (FIR) luminosities derived from IRAS.

The Role of Neutral Hydrogen in the Evolution of Sprial and Irregular Galaxies

The Hubble classification suggested for the spiral galaxies, Sa–Sb–Sc–Sm–Irr, was considered by many astronomers as an evolution succession. The version of transformation from early spirals to the late spirals and vice versa was considered. The existence of several parameters, monotonically increasing or decreasing along this succession, together with the parameters which do not depend on the structural type of the galaxies of this succession, is a confirmation of this succession to be a succession of stages of evolution. Let us consider in detail both types of parameters. About the full masses and luminosities of galaxies we can state, that except Irr and maybe Sm-galaxies there is not a clear expressed difference of mean values of these parameters for galaxies of different structural types. Irr galaxies are the systems with low masses and luminosities, but on the (M-L) diagram a part of them is obviously mixed with the late spirals. There is a strong change of the M/L ratio with changing of the structural type, though the early type galaxies on average apparently have the least values of that ratio. As monotonically changing parameters we can suggest the following three:

Southern galaxies. VII - The remarkable lenticular barred galaxy NGC 1291

view Abstract Citations (116) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Southern galaxies. VII. The remarkable lenticular barred galaxy NGC 1291. de Vaucouleurs, G. Abstract The lenticular barred galaxy NOC 1291 is the largest example of revised type (R) SB(s)0/a at the transition stage between late lenticulars and early spirals. The central lens (12 x 10 kpc) is surrounded by a large, semidetached outer ring (21 x 19 kpc) from which emerge two faint spiral arms showing incipient resolution at 20.5.In the nuclear region at the center of the primary bar (10 x 2.5 kpc), a secondary bar (1.8 x 0.2 kpc) and secondary nucleus (0.5 x 0.4 kpc) have been detected, repeating the primary lens-bar-nucleus pattern on a smaller scale approximating the ratio of the Jeans lengths. Other examples suggest that this repetitive pattern may be typical. Detailed surface photometry from long- and photographs with the Mount Stromlo 75-cm reflector and the McDonald 205-cm reflector is presented (isophotes, luminosity profiles, and photometric parameters). The total apparent magnitude m(B) = 9.37 (photoelectrically calibrated) and maximum dimensions 20' x 18' (at the detection threshold u 28.2 mag 5-2 - 0.3 Q0 ) correspond to MT(B) = -20.63 and = 52 kpc, with (B - V)r = 0.92, (U - B)r = 0.47, if rn - M = 30.0 and A = 8.9 Mpc (estimated from brightest stars and redshifr). The average surface brightness in the "dark" zone between the lens and the ring is about = 24.5 mag 2 10 at an average radius r 8 kpc from the center; the average maximum brightness in the ring is only slightly greater, about 24.0 mag s The effective equivalent radius of the isophote enclosing half the total flux is r* = 1;54 = 4.0 kpc, the same as for M31, and indicating a giant system. The spheroidal component obeying the r114 law dominates the light distribution within the lens and contributes 57 percent of the total luminosity; if it is valid up to r = 0, the true central brightness may be as high as uB(0) = 13.46 mag 2 = 2.2 x i0 . The flat component contributing to the lens and dominant in the ring does not obey the simple exponential distribution previously found in the disks of late-type spirals. The nuclear spectrum observed in the blue region at medium resolution (Mount Stromlo) and in the red region at low resolution with an image-tube spectrograph (McDonald) is a typical K-type, approximating G5 at H and K and KO III at Hy with weak 3727 emission and no H . The mean heliocentric radial velocity from three optical and one radio observations is V = + 830 km s . The total mass, neutral hydrogen mass, and massluminosity ratio estimated from corrected values of the 21-cm line parameters given by Lewis and from an optical upper limit to the velocity dispersion ( <200 km s1) are 931T 1 x 10119)lo, with 9flH/ 0.025 and 93tj B 4. These values are about normal for type 50/a (t = 0). The frequency of outer ring structures around the main bodies of galaxies of different types is discussed in an Appendix; such structures are observed only around lenticulars and spirals earlier than Sc with a sharp maximum at 80/a. Subject headings: galactic structure galaxies, individual galaxies, photometry of Publication: The Astrophysical Journal Supplement Series Pub Date: June 1975 DOI: 10.1086/190341 Bibcode: 1975ApJS...29..193D Keywords: Astronomical Photometry; Galactic Nuclei; Galactic Structure; Stellar Luminosity; Calibrating; Color; Galactic Evolution; Graphs (Charts); Isophotes; Morphological Indexes; Spiral Galaxies; Stellar Spectra; Tables (Data); Astronomy full text sources ADS | data products SIMBAD (4) NED (2) Related Materials (7) Part 1: 1961ApJ...133..405D Part 2: 1962ApJ...136..107D Part 3: 1963ApJ...137..720D Part 4: 1963ApJ...138..934D Part 5: 1964ApJ...139..899D Part 6: 1964ApJ...140..399D Part 7: 1973ApJ...181...31D