Sb Galaxies Research Articles

Bias Properties of Extragalactic Distance Indicators. VIII. \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $H_{0}$ \end{document} from Distance–limited Luminosity Class and Morphological Type–Specific Luminosity Functions for Sb, Sbc, and Sc Galaxies Calibrated Using Cepheids

Relative, reduced to absolute, magnitude distributions are obtained for Sb, Sbc, and Sc galaxies in the flux-limited Revised Shapley-Ames Catalog (RSA2) for each van den Bergh luminosity class (L), within each Hubble type (T). The method to isolate bias-free subsets of the total sample is via Spaenhauer diagrams, as in previous papers of this series. The distance-limited type and class-specific luminosity functions are to numbers of galaxies per unit volume (105 Mpc3), rather than being left as relative functions, as in Paper V. The functions are calculated using kinematic absolute magnitudes, based on an arbitrary trial value of H0 = 50. Gaussian fits to the individual functions are listed for each T and L subclass. As in Paper V, the data can be freed from the T and L dependencies by applying a correction of 0.23T + 0.5L to the individual absolute magnitudes. Here, T = 3 for Sb, 4 for Sbc, and 5 for Sc galaxies, and the L values range from 1 to 6 as the luminosity class changes from I to III-IV. The total luminosity function, obtained by combining the volume-normalized Sb, Sbc, and Sc individual luminosity functions, each corrected for the T and L dependencies, has an rms dispersion of 0.67 mag, similar to much of the Tully-Fisher parameter space. Absolute calibration of the trial kinematic absolute magnitudes is made using 27 galaxies with known T and L that also have Cepheid distances. This permits the systematic correction to the H0 = 50 kinematic absolute magnitudes of 0.22 ± 0.12 mag, giving The Cepheid are based on the Madore/Freedman Cepheid period-luminosity (PL) zero point that requires (m - M)0 = 18.50 for the LMC. Using the modern LMC modulus of (m - M)0 = 18.58 requires a 4% decrease in H0, giving a final value of H0 = 53 ± 7 (external) by this method. These values of H0, based here on the method of luminosity functions, are in good agreement with (1) H0 = 55 ± 5 by Theureau and coworkers from their bias-corrected Tully-Fisher method of normalized distances for field galaxies; (2) H0 = 56 ± 4 from the method through the Virgo Cluster, as corrected to the global kinematic frame (Tammann and coworkers); and (3) H0 = 58 ± 5 from Cepheid-calibrated Type Ia supernovae (Saha and coworkers). Our value here also disagrees with the final value from the NASA Key Project group value of H0 = 70 ± 7. Analysis of the total flux-limited sample of Sb, Sbc, and Sc galaxies in the RSA2 by the present method, but uncorrected for selection bias, would give an incorrect value of H0 = 71 using the same Cepheid calibration. The effect of the bias is pernicious at the 30% level; either it must be corrected by the methods in the papers of this series, or the data must be restricted to the distance-limited subset of any sample, as is done here.

A Kinematic Link Between Boxy Bulges, Stellar Bars, and Nuclear Activity in NGC 3079 and NGC 4388

We present direct kinematic evidence for bar streaming in two active galaxies with boxy stellar bulges. The Hawaii Imaging Fabry-Perot Interferometer was used on the Canada-France-Hawaii 3.6-m telescope and the University of Hawaii 2.2-m telescope to derive the two-dimensional velocity field of the line-emitting gas in the disks of the Sc galaxy NGC 3079 and the Sb galaxy NGC 4388. In contrast to previous work based on long-slit data, the detection of the bar potential from the Fabry-Perot data does not rely on the existence of inner Lindblad resonances or strong bar-induced shocks. Simple kinematic models which approximate the intrinsic gas orbits as nonintersecting, inclined elliptical annuli that conserve angular momentum characterize the observed velocity fields. In NGC 3079, bar streaming motions with moderately eccentric orbits (e = b/a approx. 0.7) aligned along PA = 130 deg. intrinsic to the disk (PA = 97 deg. on the sky) are detected out to R(sub b) = 3.6 kpc. The orbits become increasingly circular beyond that radius (e = 1 at R(sub d) approx. = 6 kpc). The best model for NGC 4388 includes highly eccentric orbits (e approx. 0.3) for R(sub) less than or equal to 1.5 kpc which are aligned along PA = 135 deg. intrinsic to the disk (PA = 100 deg. on the sky). The observed spiral arms are produced by having the orbits become increasingly circular from the ends of the bar to the edge of the disk (R(sub d) approx. = 5 kpc), and the intrinsic bar PA shifting from 135 deg. to 90 deg.. Box-shaped bulges in both NGC 3079 and NGC 4388 are confirmed using new near-infrared images to reduce dust obscuration. Morphological analysis of starlight in these galaxies is combined with the gas kinematics derived from the Fabry-Perot spectra to test evolutionary models of stellar bars that involve transitory boxy bulges, and to quantify the importance of such bars in fueling active nuclei. Our data support the evolutionary bar models, but fail to prove convincingly that the stellar bars in NGC 3079 and NGC 4388 directly trigger or sustain the nuclear activity.

Investigation of barred galaxies. V. Surroundings of SB and SA galaxies

Using lists of bright galaxies with and without a bar, as well as the Lyon-Meudon Extragalactic Data Set (LEDA), the surroundings of SB and SA galaxies have been investigated and some differences between them have been found.

Central Kinematics and Rotation Curve of the Sb Galaxy NGC 4527 in CO, Hα and [N II] Lines

We have obtained interferometer observations of the central region of the Sb galaxy NGC 4527 in the CO (J = 1–0) line emission using the Nobeyama Millimeter Array. We also obtained optical (Hα, [N II]) spectroscopy using the Okayama 188-cm reflector along the major axis. The kinematical structure and the distribution of H II regions show symmetry around the nucleus, while the distribution of molecular gas is asymmetric. The molecular-gas mass shares only 10% of the dynamical mass in the central 1 kpc radius region. Using position-velocity diagrams, we have derived a center-to-disk rotation curve. It rises steeply in the central region, attaining a maximum of about 250 km s−1 at 400 pc radius, and then decreases to a minimum at 2 kpc radius, followed by a disk and outer flat part. The rotation curve may provide us with the most similar case to that of the Milky Way Galaxy.

Central Rotation Curves of Spiral Galaxies

We present high-resolution central-to-outer rotation curves for Sb, SBb, Sc, and SBc galaxies. We discuss their general characteristics, particularly their central behavior, as well as dependencies on morphological types, activity, and peculiarity. The rotation curves generally show a steep nuclear rise and high-velocity central rotation, followed by a broad maximum in the disk and then a flat rotation due to the massive halo. Since the central high velocity and steep rise are common to all massive galaxies, they cannot be due to noncircular motions. Disk rotation curves of barred galaxies show larger dispersion than those of normal galaxies, probably because of noncircular motions. Interacting galaxies often show perturbed outer rotation curves, while their central rotation shows no particular peculiarity. In addition, central activities, such as starbursts and active galactic nuclei, appear to show no particular correlation with the property of rotation curves. This would suggest that the central activities are triggered by a more local effect than the global dynamical property.

Galactic‐Scale Outflow and Supersonic Ram‐Pressure Stripping in the Virgo Cluster Galaxy NGC 4388

The Hawaii Imaging Fabry-Perot Interferometer (HIFI) on the University of Hawaii 2.2 m telescope was used to map the Hα and [O III] λ5007 emission-line profiles across the entire disk of the edge-on Sb galaxy NGC 4388. We confirm a rich complex of highly ionized gas that extends ~4 kpc above the disk of this galaxy. Low-ionization gas associated with star formation is also present in the disk. Evidence for bar streaming is detected in the disk component and is discussed in a companion paper. Nonrotational blueshifted velocities of 50-250 km s-1 are measured in the extraplanar gas northeast of the nucleus. The brighter features in this complex tend to have more blueshifted velocities. A redshifted cloud is also detected 2 kpc southwest of the nucleus. The velocity field of the extraplanar gas of NGC 4388 appears to be unaffected by the inferred supersonic (Mach number M ≈ 3) motion of this galaxy through the ICM of the Virgo cluster. We argue that this is because the galaxy and the high-|z| gas lie behind a Mach cone with opening angle ~80°. The shocked ICM that flows near the galaxy has a velocity of ~500 km s-1 and exerts insufficient ram pressure on the extraplanar gas to perturb its kinematics. We consider several explanations of the velocity field of the extraplanar gas. Velocities, especially blueshifted velocities on the north of the galaxy, are best explained as a bipolar outflow that is tilted by >12° from the normal to the disk. The observed offset between the extraplanar gas and the radio structure may be due to buoyancy or refractive bending by density gradients in the halo gas. Velocity substructure in the outflowing gas also suggests an interaction with ambient halo gas.

The pattern speed of the bar in NGC 4596

The pattern speed is a defining parameter of any barred galaxy. A large number of model-dependent techniques have therefore been developed to derive the pattern speed. However, the only model-independent technique for measuring this quantity—the Tremaine-Weinberg method—has hitherto been applied to just one case, the SB0 galaxy NGC 936. In this paper, we apply the technique to a second system, the SBa galaxy NGC 4596. The resulting estimate for the pattern speed is Ωp=52±13 km s−1 kpc−1. This result is corroborated by a spectrum obtained along the major axis of the bar in this system. The corotation radius associated with this pattern speed lies just beyond the end of the bar indicating a fast bar. Combining the bar major-axis spectra with data obtained from a Hubble Space Telescope WFPC2 image, we also find strong evidence for a nuclear disc.

NGC 7331: The Galaxy with the Multicomponent Central Region

We present the results of the spectral investigation of the regular Sb galaxy NGC 7331 with the Multi-Pupil Field Spectrograph of the 6 m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The absorption-line indices Hβ, Mgb, and Fe are mapped to analyze the properties of the stellar populations in the circumnuclear region of the galaxy. The central part of the disk inside ~3'' (200 pc)—or a separate circumnuclear stellar gaseous disk as it is distinguished by decoupled fast rotation of the ionized gas—is very metal rich, rather young (~2 billion yr old), and its solar magnesium-to-iron ratio evidences for a very long duration of the last episode of star formation there. However, the gas excitation mechanism now in this disk is shocklike. The starlike nucleus probably experienced a secondary star formation burst too: its age is 5 billion yr, much younger than the age of the circumnuclear bulge. But [Mg/Fe] = +0.3, and only solar global metallicity implies that the nuclear star formation burst has been much shorter than that in the circumnuclear disk. The surrounding bulge is rather old, 9–14 billion yr, and moderately metal poor. The rotation of the stars and gas within the circumnuclear disk is axisymmetric, although its rotation plane may be slightly inclined to the global plane of the galaxy. Outside the circumnuclear disk the gas may experience noncircular motions, and we argue that the low-contrast extended bulge of NGC 7331 may be triaxial.

The Central Regions of M81

High–angular resolution near-infrared images obtained with the Canada-France-Hawaii Telescope adaptive optics system are combined with archival Hubble Space Telescope data to investigate the central regions of the nearby Sb galaxy M81 (NGC 3031). The spectral-energy distribution of the circumnuclear region, which extends out to 15 (∼24 pc if μ0 = 27.5) from the nucleus, can be modeled as a combination of an old metal-rich population and emission from hot dust. Thermal emission, which has been attributed to hot dust, has been detected near other active galactic nuclei, and simple models indicate that hot dust can account for ∼20% of the light in K within 05 of the M81 nucleus. An elongated structure with MV ∼ -7, which may be an area of active star formation, is detected 045 from the nucleus. At distances in excess of 15 from the nucleus, the J-K color of the M81 bulge is not significantly different from what is seen in M31. The HST data are also used to search for bright globular clusters within 2 kpc of the center of M81. The area within 0.26 kpc of the M81 nucleus is largely devoid of bright globular clusters, in agreement with what is seen in the central regions of the Galaxy and M31. However, our survey indicates that there may be ∼45 ± 12 globular cluster candidates with MV ≤ -7 within 2 kpc of the galaxy center, which is consistent with what would be infrared from the Milky Way cluster system after adjusting for differences in the total number of clusters.

A 180 Kiloparsec Tidal Tail in the Luminous Infrared Merger Arp 299

We present VLA H I observations and University of Hawaii 88 inch (2.2 m) deep optical B- and R-band observations of the IR-luminous merger Arp 299 (= NGC 3690 + IC 694). These data reveal a gas-rich (MH I = 3.3 × 109 M⊙) optically faint (μB 27 mag arcsec-2, μR 26 mag arcsec-2) tidal tail with a length of over 180 kpc. The size of this tidal feature necessitates an old interaction age for the merger (750 Myr since first periapse), which is currently experiencing a very young starburst (20 Myr). The observations reveal a most remarkable structure within the tidal tail: it appears to be composed of two parallel filaments separated by approximately 20 kpc. One of the filaments is gas-rich with little if any starlight, while the other is gas-poor. We believe that this bifurcation results from a warped disk in one of the progenitors. The quantities and kinematics of the tidal H I suggest that Arp 299 results from the collision of a retrograde Sab–Sb galaxy (IC 694) and a prograde Sbc–Sc galaxy (NGC 3690) that occurred 750 Myr ago and will merge into a single object in roughly 60 Myr. We suggest that the present IR-luminous phase in this system is due in part to the retrograde spin of IC 694. Finally, we discuss the apparent lack of tidal dwarf galaxies within the tail.

Radio Continuum Observations of NGC 1961: Interaction with the Intergalactic Medium or the Remnant of a Merger?

We present new radio continuum images of the supermassive, peculiar galaxy NGC 1961 at 1.5, 4.9, 8.4 and 15 GHz. NGC 1961 (Arp 184) is a very massive (dynamical mass > 1012M⊙) Sb galaxy with a peculiar and asymmetric optical appearance. Furthermore, it exhibits an unusual, asymmetric HI distribution with an extensive wing of gas extending 30 kpc to the north-west and a sharp edge to the south-east (Shostak et al. 1982).

Environmental Extremists in the Virgo Cluster

Many types of galaxy interactions have been posited to occur in clusters, although it remains unclear which processes actually occur, and which ones might help explain the tendency for early type galaxies to inhabit high density environments, or cause the rapid evolution of cluster galaxies (e.g., Dressler et al. 1997). With these questions in mind, we have been conducting an environmental inventory of galaxies in the Virgo Cluster. Our approach is to combine surveys of spirals and S0s with detailed studies of the most interesting and peculiar galaxies. In this paper, we describe two main points. 1.) There is a population of spiral galaxies in the Virgo cluster with the small central light concentrations (bulge-to-disk ratios, or B/D's) characteristic of isolated Sb and Sc galaxies, but global star formation rates lower than those of isolated spirals of any Hubble class (Sa-Sc). These Virgo galaxies are generally classified as “early type” (e.g. Sa), and thus contribute to the morphology-density relationship. 2.) There areseveral typesof environmental interactions occurring in Virgo, including low velocity tidal interactions and mergers, high velocity tidal interactions and collisions, HI accretion, and ICM-ISM stripping. We discuss examples of some of these interactions.

Nuclear-to-disk rotation curves and mass-to-luminosity ratio in galaxies

High-resolution nuclear-to-outer rotation curves for Sb, SBb, Sc, and SBc galaxies generally show a steep nuclear rise and flat rotation from the disk to the halo. The high-velocity central rotation indicates massive cores within bulges. Since this characteristic is common to most galaxies, the high-velocity central rotation cannot be due to a particular orientation of non-circular motion. Using these rotation curves, we derive the distributions of surface-mass density, and compare them directly with observed surface-luminosity distributions. The mass-to-luminosity ratio (M/L) increases from the outer bulge to the disk, indicating that the outer disk is already dominated by dark-mass. It, then, increases more rapidly toward the outer optical edge, indicating the massive halo. In the central regions of some galaxies, the M/L increases steeply toward the nucleus, reaching a value an order of magnitude greater in the central 100 pc region than that in the disk, which may indicate a massive core of radius ∼ 100 parsecs and mass of ∼ 10 9 M ⊙. The core may be an object linking a bulge and a black hole at the nucleus.

Investigation of Dust Extinction in Sb Galaxies using Scale Length Ratios

For a sample of 16 Sb galaxies, disc scale lengths rD in B and I are investigated in order to study the dust content. The ratios rD(B)/rD(I) increase from 1.0 for face-on galaxies to 1.5 for edge-on galaxies. Scale length ratios derived from model images increase from face-on to edge-on view by ≤ 10% only, regardless of whether the model galaxies are optically thin or optically thick.

Barred galaxies. IV. Comparative statistics on SB and SA galaxies in the radio and x-ray ranges

The radio and xray properties of spiral galaxies with and without a bar are discussed on the basis of complete samples that we have compiled. The two types of spirals are shown not to differ from one another in emission power in the two indicated ranges. In the case of SB galaxies, the luminosities in the IR, radio, and xray ranges are closely related. The spectral indices of SB and SA galaxies in the 1.4–5 GHz range are the same, on the average. In the case of barred galaxies, however, a definite dependence is observed between the spectral index and both the IR and × ray luminosities, i.e., the spectral index increases as both luminosities increase. It is assumed that this is caused by the bar itself, which stimulates star formation in a barred galaxy.

Systematics of Dark Halos in High Surface Brightness Spiral Galaxies

A study of mass distributions in 22 spiral galaxies, with rotation curves taken from the literature and Hubble types ranging from Sa to Sd, is presented. It is demonstrated that a relation of the form between the mass distribution of the luminous components M(r) and that of the dark halo Md(r) is consistent with the observed kinematics with only the dark-to-visible mass ratio displaying significant variations between galaxies. The parameter γ, which is correlated with Mdyn/Mlum, characterizes the relative importance of the dark-to-luminous mass. The model M/L ratio of the stellar component, M/LB(stars), is correlated with the observed B - V color. In our sample the average model ⟨M/LB(stars)⟩ of Sb galaxies is 2.7 M⊙ L for an average color ⟨(B - V)0⟩ = 0.71, that of the Sc's is ⟨M/LB(stars)⟩ = 1.5 M⊙ L for ⟨(B - V)0⟩ = 0.54, both values being in very good agreement with population synthesis models. A large part of the intrinsic scatter in the Tully-Fisher relation is due to the spread in γ. The relation of coupling accounts for the disk-halo conspiracy in HSB spirals and is also valid in LSB dwarf galaxies. Its universality in disk rotating systems implies the existence of a physical mechanism responsible for the continuity between visible and dark mass distributions.

Barred galaxies. III. Comparative statistics on SB and SA galaxies in the infrared

The characteristics of galaxies with and without a bar in the infrared range are compared, using two complete samples that we have compiled. The data obtained show that star formation occurs more actively in barred galaxies than in galaxies without a bar, which it is natural to believe is a consequence of the presence of the bar itself.

Internal extinction of disc galaxies - I. High-resolution extinction map of NGC 6946

Traditionally, it has been believed that extinction effects due to dust within the interstellar medium of external galaxies are rather small and can largely be ignored. Over the last 10 years, however, considerable doubt has been cast over the evidence to support this comfortable idea, and it has become clear that a more detailed analysis is required. Here, a new technique for mapping the extinction in disc galaxies with high resolution is presented. This technique has been applied to the Sc galaxy NGC 6946. The results show that dust extinction significantly affects both the overall brightness and appearance of the galaxy. The total extinction is found to be AB=0.45 – somewhat larger than the value of AB=0.2 usually quoted for an Sc galaxy. When corrected for dust the morphology more closely resembles that of an Sb galaxy rather than an Sc galaxy. The most surprising result of this work is finding interarm regions that suffer high extinction. It appears that these regions appear faint because of the high extinction and not as a result of low stellar density. There are also interarm regions that suffer little extinction; these are therefore truly regions of low stellar density.

Extended Ionized Gas Emission and Kinematics of the Compact Group Galaxies in Hickson Compact Group 16: Signatures of Mergers

We report on kinematic observations of Hα emission from four late-type galaxies of Hickson Compact Group 16 (H16a, b, c, d) obtained with a scanning Fabry-Perot interferometer and samplings of 16 km s-1 and 1''. The velocity fields show kinematic peculiarities for three of the four galaxies: H16b, H16c, and H16d. Misalignments between the kinematic and photometric axes of gas and stellar components (H16b-H16d), double gas systems (H16c) and severe warping of the kinematic major axis (H16b and H16c) were some of the peculiarities detected. We conclude that major merger events have taken place in at least two of the galaxies of the group, H16c and H16d, based on their significant kinematic peculiarities, their double nuclei, and their high infrared luminosities. Their Hα gas content is strongly spatially concentrated; H16d contains a peculiar barlike structure confined to the inner ~1 h-1 kpc region. These observations are in agreement with predictions of simulations, namely, that the gas flows toward the galaxy nucleus during mergers, forms bars, and fuels the central activity. Galaxy H16b, an Sb galaxy, also presents some of the kinematic evidence for past accretion events. Its gas content, however, is very sparse, limiting our ability to find other kinematic merging indicators, if they are present. We find that the merger remnants in the compact group HCG 16 have significantly smoother optical profiles than isolated mergers, i.e., they show an amorphous morphology and no signs of tidal tails. Tidal arms and tails formed during the mergers may have been stripped by the group potential, or, alternatively, they may have never been formed. The velocity field of the galaxy H16a shows grand-design isovelocity lines with no signs of disturbances inside a radius of ~R25. This result is contrary to expectations given that the galaxy has a high infrared luminosity, central activity, tidal tails at large radii, and is embedded in a common group envelope observed in H I and X-rays. The normality of the velocity field suggests that this galaxy may be a fairly recent acquisition of the compact group. Our observations suggest that HCG 16 may be a young compact group in formation through the merging of close-by objects in a dense environment.

Barred galaxies. II. Comparative statistics on SB and SA galaxies in visible light

Various characteristics of galaxies with and without a bar are compared in two complete samples compiled by the authors. It is found that the two types of spiral galaxies hardly differ from each other in a number of parameters and properties, such as nuclear activity and degree of concentration in groups. Star formation evidently occurs more efficiently in barred galaxies, however. Bars are encountered more often in intermediate and late subtypes of disk galaxies. Barred galaxies in groups are redder, on the average, than those outside of groups. Luminosity functions are constructed both for galaxies with and without bars.