Function Of Hubble Type Research Articles

Bar Fraction in Early- and Late-type Spirals

Abstract Bar fractions depend on the properties of the host galaxies, which are closely related to the formation and evolution of bars. However, observational studies do not provide consistent results. We investigate the bar fraction and its dependence on the properties of the host galaxies by using three bar classification methods: visual inspection, an ellipse fitting method, and Fourier analysis. Our volume-limited sample consists of 1698 spiral galaxies brighter than M r = −15.2 with z < 0.01 from the Sloan Digital Sky Survey/DR7 visually classified by Ann et al. We first compare the consistency of classification among the three methods. Automatic classifications detect visually determined, strongly barred galaxies with the concordance of 74% to 85%. However, they have some difficulty in identifying bars, in particular in bulge-dominated galaxies, which affects the distribution of bar fraction as a function of Hubble type. We obtain, for the same sample, different bar fractions of 63%, 48%, and 36% by visual inspection, ellipse fitting, and Fourier analysis, respectively. The difference is mainly due to how many weak bars are included. Moreover, we find a different dependence of bar fraction on Hubble type for strong versus weak bars: SBs are preponderant in early-type spirals, whereas SABs are in late-type spirals. This causes a contradictory dependence on host galaxy properties when different classification methods are used. We propose that strong bars and weak bars experience different processes for their formation, growth, and dissipation by interacting with different inner galactic structures of early-type and late-type spirals.

The EDGE-CALIFA Survey: Interferometric Observations of 126 Galaxies with CARMA

Abstract We present interferometric CO observations, made with the Combined Array for Millimeter-wave Astronomy (CARMA) interferometer, of galaxies from the Extragalactic Database for Galaxy Evolution survey (EDGE). These galaxies are selected from the Calar Alto Legacy Integral Field Area (CALIFA) sample, mapped with optical integral field spectroscopy. EDGE provides good-quality CO data (3σ sensitivity before inclination correction, resolution ∼1.4 kpc) for 126 galaxies, constituting the largest interferometric CO survey of galaxies in the nearby universe. We describe the survey and data characteristics and products, then present initial science results. We find that the exponential scale lengths of the molecular, stellar, and star-forming disks are approximately equal, and galaxies that are more compact in molecular gas than in stars tend to show signs of interaction. We characterize the molecular-to-stellar ratio as a function of Hubble type and stellar mass and present preliminary results on the resolved relations between the molecular gas, stars, and star-formation rate. We then discuss the dependence of the resolved molecular depletion time on stellar surface density, nebular extinction, and gas metallicity. EDGE provides a key data set to address outstanding topics regarding gas and its role in star formation and galaxy evolution, which will be publicly available on completion of the quality assessment.

The Herschel Reference Survey

ABSTRACTThe Herschel Reference Survey is a Herschel guaranteed time key project and will be a benchmark study of dust in the nearby universe. The survey will complement a number of other Herschel key projects including large cosmological surveys that trace dust in the distant universe. We will use Herschel to produce images of a statistically-complete sample of 323 galaxies at 250, 350, and 500 μm. The sample is volume-limited, containing sources with distances between 15 and 25 Mpc and flux limits in the K band to minimize the selection effects associated with dust and with young high-mass stars and to introduce a selection in stellar mass. The sample spans the whole range of morphological types (ellipticals to late-type spirals) and environments (from the field to the center of the Virgo Cluster) and as such will be useful for other purposes than our own. We plan to use the survey to investigate (i) the dust content of galaxies as a function of Hubble type, stellar mass, and environment; (ii) the connection between the dust content and composition and the other phases of the interstellar medium; and (iii) the origin and evolution of dust in galaxies. In this article, we describe the goals of the survey, the details of the sample and some of the auxiliary observing programs that we have started to collect complementary data. We also use the available multifrequency data to carry out an analysis of the statistical properties of the sample.

The fundamental properties of galaxies and a new galaxy classification system

We present in this paper a new three-dimensional galaxy classification system designed to account for the diversity of galaxy properties in the nearby universe. To construct this system we statistically analyse a sample of >22 000 galaxies at v < 15 000 km s−1 (z < 0.05) with Spearman rank and principal-component analyses (PCAs). Fourteen major galaxy properties are considered, including: Hubble type, size, colour, surface brightness, magnitude, stellar mass, internal velocities, H i gas content and an index that measures dynamical disturbances. We find, to a high degree, that most galaxy properties are correlated, with in particular Hubble type, colour and stellar mass all strongly related. We argue that this tight three-way correlation is a result of evolutionary processes that depend on galaxy mass, as we show that the relation between colour and mass is independent of Hubble type. Various PCAs reveal that most of the variation in nearby galaxy properties can be accounted for by eigenvectors dominated by (i) the scale of a galaxy, such as its stellar mass, (ii) the spectral type and (iii) the degree of dynamical disturbances. We suggest that these three properties: mass, star formation and interactions/mergers are the major features that determine a galaxy's physical state, and should be used to classify galaxies. As shown by Conselice et al., these properties are measurable within the CAS (concentration, asymmetry, clumpiness) structural system, thus providing an efficient mechanism for classifying galaxies in optical light within a physical meaningful framework. We furthermore discuss the fraction and number density of galaxies in the nearby universe as a function of Hubble type, for comparison with higher redshift populations.

An inventory of supershells in nearby galaxies: first results from THINGS

AbstractThe HI Nearby Galaxy Survey (THINGS), is a 21–cm HI line survey of a sample of 34 nearby (3–10 Mpc) galaxies (Walter et al. 2005). The observations were carried out with the VLA and have a velocity resolution of 5 km s−1 or better and an angular resolution of 7″ which at this distance range corresponds to a linear resolution of 100–300 pc. One of the primary goals of THINGS is to look at the fine–scale structure of the Interstellar Medium (ISM) and examine how it varies as a function of Hubble type, star formation rate, galaxy mass, metallicity, etc. We present one of the first science results from this project, an inventory of HI shells in the galaxies NGC 628, NGC 3184, and NGC 6946.

Massive Star Formation Rates and Radial Distributions from Hα Imaging of 84 Virgo Cluster and Isolated Spiral Galaxies

The massive star formation properties of 55 Virgo Cluster and 29 isolated S0-Scd bright (MB ≤ -18) spiral galaxies are compared via analyses of R and Hα surface photometry and integrated fluxes as functions of Hubble type and central R light concentration (bulge-to-disk ratio). In the median, the total normalized massive star formation rates (NMSFRs) in Virgo Cluster spiral galaxies are reduced by factors of up to 2.5 compared with isolated spiral galaxies of the same type or concentration, with a range from enhanced (up to 2.5 times) to strongly reduced (up to 10 times). Within the inner 30% of the optical disk, Virgo Cluster and isolated spiral galaxies have similar ranges in NMSFRs, with similar to enhanced (up to 4 times) median NMSFRs for Virgo galaxies. NMSFRs in the outer 70% of the optical disk are reduced in the median by factors of up to 9 for Virgo Cluster spiral galaxies, with more severely reduced star formation at progressively larger disk radii. Thus, the reduction in total star formation of Virgo Cluster spiral galaxies is caused primarily by spatial truncation of the star-forming disks. The correlation between H I deficiency and R light central concentration is much weaker than the correlation between H I deficiency and Hubble type. The previously observed systematic difference in H I spatial distributions and kinematics between early- and late-type spiral galaxies in the Virgo Cluster is at least partially due to the misleading classification of stripped spiral galaxies as early types. Intracluster medium-interstellar medium stripping of the gas from spiral galaxies is likely responsible for the truncated star-forming disks of Virgo Cluster spiral galaxies. This effect may be responsible for a significant part of the morphology-density relationship, in that a large fraction of Virgo Cluster galaxies classified as Sa galaxies are H I-deficient galaxies with truncated star-forming disks rather than galaxies with large bulge-to-disk ratios.

Structure of Disk‐dominated Galaxies. II. Color Gradients and Stellar Population Models

We investigate optical and near-IR color gradients in a sample of 172 low-inclination galaxies spanning Hubble types S0-Irr. The colors are compared with stellar population synthesis models from which luminosity-weighted average ages and metallicities are determined. We explore the effects of different underlying star formation histories and additional bursts of star formation. Our results are robust in a relative sense under the assumption that our galaxies shared a similar underlying star formation history and that no bursts involving more than ∼10% of the galaxy mass have occurred in the past 1-2 Gyr. Because the observed gradients show radial structure, we measure "inner" and "outer" disk age and metallicity gradients. Trends in age and metallicity and their gradients are explored as a function of Hubble type, rotational velocity, total near-IR galaxy magnitude, central surface brightness, and scale length. We find strong correlations in age and metallicity with Hubble type, rotational velocity, total magnitude, and central surface brightness in the sense that earlier-type, faster rotating, more luminous, and higher surface brightness galaxies are older and more metal-rich, suggesting an early and more rapid star formation history for these galaxies. The increasing trends with rotational velocity and total magnitude level off for Vrot ≳ 120 km s-1 and MK ≲ -23 mag, respectively. This effect is stronger for metallicity (than age), which could reflect a threshold potential above which all metals are retained and thus metallicity saturates at the yield. Outer disk gradients are found to be weaker than the inner gradients as expected for a slower variation of the potential and surface brightness in the outer parts. We find that stronger age gradients are associated with weaker metallicity gradients. Trends in gradients with galaxy parameters are compared with model predictions: these trends do not agree with predictions of semianalytic models of hierarchical galaxy formation, possibly owing to the effect of bar-induced radial flows. The observed trends are in agreement with chemo-spectrophotometric models of spiral galaxy evolution based on CDM-motivated scaling laws but none of the hierarchical merging characteristics, implying a strong dependence of the star formation history of spiral galaxies on the galaxy potential and halo spin parameter.

Observational Constraints on Disk Heating as a Function of Hubble Type

Current understanding of the secular evolution of galactic disks suggests that this process is dominated by two or more mechanisms, which increase the random motions of stars in the disk. In particular, the gravitational influence of giant molecular clouds and irregularities in the spiral potential have been proposed to explain the observed velocity dispersions in the solar neighborhood. Each of these mechanisms acts on different components of the stellar velocity, which affects the ratio σz/σR of the vertical and radial components differently. Since the relative strengths of giant molecular clouds and spiral irregularities vary with Hubble type, a study of σz/σR as function of Hubble type has the potential to provide strong constraints on disk heating mechanisms. We present major- and minor-axis stellar kinematics for four spiral galaxies of Hubble type from Sa to Sbc and use the data to infer the ratios σz/σR in the galaxy disks. We combine the results with those for two galaxies studied previously with the same technique, with Milky Way data, and with estimates obtained using photometric techniques. The results show that σz/σR is generally in the range 0.5–0.8. There is a marginally significant trend of decreasing σz/σR with advancing Hubble type, consistent with the predictions of disk heating theories. However, the errors on individual measurements are large, and the absence of any trend is consistent with the data at the 1 σ level. As a by-product of our study, we find that three of the four galaxies in our sample have a central drop in their stellar line-of-sight velocity dispersion, a phenomenon that is increasingly observed in spiral galaxies.

Molecular gas in the central regions of the latest-type spiral galaxies

Using the IRAM 30 m telescope, we have surveyed an unbiased sample of 47 nearby spiral galaxies of very late (Scd-Sm) Hubble-type for emission in the 12 CO(1−0) and (2−1) lines. The sensitivity of our data (a few mK) allows detection of about 60% of our sample in at least one of the CO lines. The median detected H2 mass is 1.4 × 10 7 Mwithin the central few kpc, assuming a standard conversion factor. We use the measured line intensities to complement existing studies of the molecular gas content of spiral galaxies as a function of Hubble-type and to significantly improve the statistical significance of such studies at the late end of the spiral sequence. We find that the latest-type spirals closely follow the correlation between molecular gas content and galaxy luminosity established for earlier Hubble types. The molecular gas in late-type galaxies seems to be less centrally concentrated than in earlier types. We use Hubble Space Telescope optical images to correlate the molecular gas mass to the properties of the central galaxy disk and the compact star cluster that occupies the nucleus of most late-type spirals. There is no clear correlation between the luminosity of the nuclear star cluster and the molecular gas mass, although the CO detection rate is highest for the brightest clusters. It appears that the central surface brightness of the stellar disk is an important parameter for the amount of molecular gas at the galaxy center. Whether stellar bars play a critical role for the gas dynamics remains unclear, in part because of uncertainties in the morphological classifications of our sample.

Probing the Formation and Evolution of early-type galaxies: the SAURON project

We are conducting a systematic study of a carefully selected sampleof nearby E/S0 galaxies and Sa bulges using the unique panoramic integral-fieldspectrograph SAURON, mounted at the WHT. The goal of the SAURON projectis to fully map the gaseous/stellar kinematics and the stellar populations of a representative sample of 80 early-type galaxies up to 1 Re,probing different environments (clusters, field). These data, used in combination with existing ground-based and HST observations, and fed to the theoretical machinery we have developed, will allow to determine theintrinsic dynamical structure of the galaxies. We will also measure the masses of central black holes, relate the internal dynamics to the ageand metallicity of the stellar populations, and establish the historyof metal enrichment as a function of Hubble type and environment. Some brief results on two targets observed during the SAURON campaign will serve as an illustration of the unique and high quality data we are currently gathering.

New Insights from [ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] Studies of Globular Cluster Systems. II. Analysis of 29 S0 Systems

We examine the globular cluster systems (GCSs) of a sample of 34 S0 galaxies from a WFPC2 survey in the V and I bands. Of these 34 galaxies, 29 have measurable globular cluster systems. The mean color of the GCSs of individual galaxies vary from V-I = 0.85 mag to V-I = 1.17 mag. The average color of GCSs in all 29 S0 galaxies, V-I = 1.00 ± 0.07 mag, is similar to the value of V-I = 1.04 ± 0.04 derived for ellipticals in a companion paper. The mean metallicity of a cluster system is correlated to the luminosity (or mass) of the host galaxy, but it is not dependent on the Hubble type. Our measurements of the local specific frequency, on the other hand, confirm that the cluster formation efficiency is a function of Hubble type. The mean local specific frequency of our sample within the WFPC2 field of view is 1.0 ± 0.6, lower than SN(Local) = 2.4 ± 1.8 derived for ellipticals in a similar analysis. Although we are able to confirm a bimodal color distribution in only one galaxy from the shallow snapshot images analyzed in this paper, statistical tests suggest that 10%–20% of S0s are bimodal at the present level of photometric accuracy. There are no significant trends in GCS properties with membership or location of the S0 host in a galaxy cluster. We have measured the turnover luminosity of the globular cluster luminosity function (GCLF) for the richest few GCSs and find the GCLF distances to be in agreement with other estimates. The globular clusters in S0 galaxies have average half-light radii of ≈2.6 pc, which is similar to that of other galaxies, including our own.

Hubble Space Telescope Optical-Near-Infrared Colors of Nearby R1/4and Exponential Bulges*

We have analyzed V, H, and J Hubble Space Telescope (HST) images for a sample of early- to late-type spiral galaxies and have reported elsewhere the statistical frequency of R1/4-law and exponential bulges in our sample as a function of Hubble type and the frequency of occurrence and structural properties of the resolved central nuclei hosted by intermediate- to late-type bulges and disks (see references in the text). Here we use these data to show the following:

Global Relationships Among the Physical Properties of Stellar Systems.

The kappa-space three-dimensional parameter system was originally defined for the physical properties of dynamically hot galaxies. Here we define self-consistent kappa-parameters for disk galaxies, galaxy groups and clusters, and globular clusters and project an integrated view of the major classes of self-gravitating, equilibrium stellar systems in the universe. Six different fundamental planes exist that are interrelated and interconnected - the ``cosmic metaplane.'' The kappa-3 vs. kappa-1 projection (M/L vs. Mass) views all planes edge-on, M/L increasing or constant with Mass. Within the cosmic metaplane (kappa-2 vs. kappa-1 projection), no stellar system violates the rule that kappa-1 + kappa-2 < 8, meaning the maximum volume luminosity density of stellar systems varies as a (K times M^{-4/3}; the ``zone of exclusion''). Galaxies march away from ZOE as a function of Hubble type: DHGs closest, Sm-Irr's furthest away. We test current ideas of galaxy formation via hierarchical clustering and merging and find them to be broadly consistent with the properties of the cosmic metaplane. Four key questions are raised by this study: Why do galaxy groups form a bridge between galaxy clusters and galaxies? Why do galaxies march away from the ZOE? Why are isotropic galaxies only found in a limited mass range? What causes M/L to vary so smoothly with M to produce the cosmic metaplane? This study is but the first step along a long road, limited by existing data to the B passband of major stellar systems, whose light is dominated by stars. K-band data would be high desirable, as well as data that can probe the gaseous content (cold and hot) of stellar systems, and data for other classes of stellar systems.

Near-Infrared Observations of Isophotal Twists in Barred Spiral Galaxies

view Abstract Citations (46) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Near-Infrared Observations of Isophotal Twists in Barred Spiral Galaxies Elmegreen, Debra Meloy ; Elmegreen, Bruce G. ; Chromey, Frederick R. ; Hasselbacher, David Alan ; Bissell, Bradley A. Abstract We present observations in JHK passbands for 12 barred galaxies and in BI passbands for 9 galaxies in order to study isophotal twists in early- and late-type barred spirals. We also summarize previous observations and examine high-resolution atlas images to compile data on twists as a function of Hubble type. Twists have been detected only in early-type spirals. This result is consistent with the hypothesis that only early- type bars have inner Lindblad resonances and that twists are associated with ILRs. The transition occurs around type SBbc and parallels the transition from bars with relatively flat intensity profiles to bars with exponential profiles in later types. Publication: The Astronomical Journal Pub Date: May 1996 DOI: 10.1086/117926 Bibcode: 1996AJ....111.1880E Keywords: GALAXIES: KINEMATICS AND DYNAMICS; GALAXIES: SPIRAL; GALAXIES: STRUCTURE full text sources ADS | data products NED (71) SIMBAD (40)

Bar Properties as a Function of Hubble Type

AbstractPrevious optical surface photometry of barred spiral galaxies revealed that there are two distinct types of bars: large bars tend to have a nearly constant surface brightness (”flat“ bar), while smaller bars tend to have a decreasing surface brightness with a scale length similar to the disk (”exponential“ bar). Statistically, flat bars tend to occur in early Hubble types and exponential bars in later types. Studies of resonances in spirals indicate that flat bars end inside corotation, while exponential bars end between the inner Lindblad and 4:1 resonances. Near-infrared (JHK) surface photometry of bars is presented in order to compare the stellar distributions and bar potentials in flat and exponential barred galaxies. The presence of isophotal twists in some galaxies provides additional information on resonances. The grand design and fiocculent optical structures in the two types of barred galaxies will be compared and contrasted with their near-infrared light distributions.

Abundances of H II regions in early-type spiral galaxies

view Abstract Citations (175) References (63) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Abundances of H II Regions in Early-Type Spiral Galaxies Oey, M. S. ; Kennicutt, R. C., Jr. Abstract We present an abundance study of H II regions in 15 Sa to Sb galaxies. We find that the metal abundances of the H II regions are systematically higher than those in Sc and later type galaxies, although this effect is not a function of Hubble type only. The distribution of reddening values is similar to late-type spirals, indicating that the dust levels associated with our sample of H II regions are not unusually high. This implies that the systematic changes in H II region luminosity along the Hubble sequence are due to intrinsic differences in the properties of the gas and ionizing OB associations, rather than to differences in extinction. Our data also suggest that the abundance gradients in early- type galaxies may generally be flatter than in Sc galaxies. The metallicities within our sample exhibit no correlation with galaxy mass, suggesting that mass is not the only factor driving the observed gas- phase abundances among luminous (M_B_ < - 20) spiral galaxies. We have also computed photoionization models of metal-rich (0.5-3 Z_sun_) H II regions, in order to evaluate the reliability of the Pagel & Edmunds R_23_, empirical abundance parameter in this abundance range. The results indicate that R_23_, provides a valuable means of ranking relative abundances in this regime, but systematic variations in other parameters, most notably nebular density and stellar effective temperature, introduce significant uncertainties into the abundance scales. Publication: The Astrophysical Journal Pub Date: July 1993 DOI: 10.1086/172814 Bibcode: 1993ApJ...411..137O Keywords: Abundance; H Ii Regions; Interstellar Matter; Spiral Galaxies; Stellar Temperature; Big Bang Cosmology; Galactic Evolution; Luminosity; Stellar Evolution; Vapor Phases; Astrophysics; GALAXIES: ABUNDANCES; GALAXIES: SPIRAL; ISM: H II REGIONS full text sources ADS | data products SIMBAD (15) NED (15)

Systematics of HII Rotation Curves

Systematic rotational properties of field spiral galaxies are presented, as a function of Hubble type and of luminosity. Within a Hubble type, radius, nuclear velocity gradient, rotation velocity, mass, and mass density increase with luminosity, while m/L is constant. At fixed luminosity, V(max), mass, density, and m/L decrease from Sa through Sc. These variations are so systematic that it is possible to display them on a single diagram.