Luminosities of Barred and Unbarred S0 Galaxies

Lenticular galaxies with M_B < -21.5 are almost exclusively unbarred, whereas both barred and unbarred objects occur at fainter luminosity levels. This effect is observed both for objects classified in blue light, and for those that were classified in the infrared. This result suggests that the most luminous (massive) S0 galaxies find it difficult to form bars. As a result the mean luminosity of unbarred lenticular galaxies in both B and IR light is observed to be ~0.4 mag brighter than than that of barred lenticulars. A small contribution to the observed luminosity difference that is found between SA0 and SB0 galaxies may also be due to the fact that there is an asymmetry between the effects of small classification errors on SA0 and SB0 galaxies. An E galaxy might be misclassified as an S0, or an S0 as an E. However, an E will never be misclassified an SB0, nor will an SB0 ever be called an E. This asymmetry is important because elliptical (E) galaxies are typically twice as luminous as lenticular (S0) galaxies. The present results suggest that the evolution of luminous lenticular galaxies may be closely linked to that of elliptical galaxies, whereas fainter lenticulars might be more closely associated with ram-pressure stripped spiral galaxies. Finally it is pointed out that fine details of the galaxy formation process might account for some of the differences between the classifications of the same galaxy by individual competent morphologists.Comment: Astrophysical Journal, in pres

Approaches to Automated Morphological Classification of Galaxies

There is an obvious need for automated classification of galaxies, as the number of observed galaxies increases very fast. We examine several approaches to this problem, utilising {\em Artificial Neural Networks} (ANNs). We quote results from a recent study which show that ANNs can classsify galaxies morphologically as well as humans can.Comment: 8 pages, uu-encoded compressed postscript file (containing 2 figures

Quantitative Morphology of Galaxies in the Hubble Deep Field

We measure quantitative structural parameters of galaxies in the Hubble Deep Field (HDF) on the drizzled F814W images. Our structural parameters are based on a two-component surface brightness made up of a S\'ersic profile and an exponential profile. We compare our results to the visual classification of van den Bergh et al. (1996) and the $C-A$ classification of Abraham et al. (1996a). Our morphological analysis of the galaxies in the HDF indicates that the spheroidal galaxies, defined here as galaxies with a dominant bulge profile, make up for only a small fraction, namely 8% of the galaxy population down to m$_{F814W}(AB)$ = 26.0. We show that the larger fraction of early-type systems in the van den Bergh sample is primarily due to the difference in classification of 40% of small round galaxies with half-light radii < 0\arcsecpoint 31. Although these objects are visually classified as elliptical galaxies, we find that they are disk-dominated with bulge fractions < 0.5. Given the existing large dataset of HDF galaxies with measured spectroscopic redshifts, we are able to determine that the majority of distant galaxies ($z>2$) from this sample are disk-dominated. Our analysis reveals a subset of HDF galaxies which have profiles flatter than a pure exponential profile.Comment: 35 pages, LaTeX, 18 Postscript Figures, Tables available at http://astro.berkeley.edu/~marleau/. Accepted for Publication in The Astrophysical Journa

Mid-Infrared Galaxy Morphology Along the Hubble Sequence

The mid-infrared emission from 18 nearby galaxies imaged with the IRAC instrument on Spitzer Space Telescope samples the spatial distributions of the reddening-free stellar photospheric emission and the warm dust in the ISM. These two components provide a new framework for galaxy morphological classification, in which the presence of spiral arms and their emission strength relative to the starlight can be measured directly and with high contrast. Four mid-infrared classification methods are explored, three of which are based on quantitative global parameters (colors, bulge-to-disk ratio) similar to those used in the past for optical studies; in this limited sample, all correlate well with traditional B-band classification. We suggest reasons why infrared classification may be superior to optical classification.Comment: ApJS (in press), Spitzer Space Telescope Special Issue; 13 pages, LaTeX (or Latex, etc); Figure 1ab is large, color plate; full-resolution plates in .pdf format available at http://cfa-www.harvard.edu/irac/publications

Dependence of Spiral Galaxy Distribution on Viewing Angle in RC3

The normalized inclination distributions are presented for the spiral galaxies in RC3. The results show that, except for the bin of $81^{\circ}$-$90^{\circ}$, in which the apparent minor isophotal diameters that are used to obtain the inclinations, are affected by the central bulges, the distributions for Sa, Sab, Scd and Sd are well consistent with the Monte-Carlo simulation of random inclinations within 3-$\sigma$, and Sb and Sbc almost, but Sc is different. One reason for the difference between the real distribution and the Monte-Carlo simulation of Sc may be that some quite inclined spirals, the arms of which are inherently loosely wound on the galactic plane and should be classified to Sc galaxies, have been incorrectly classified to the earlier ones, because the tightness of spiral arms which is one of the criteria of the Hubble classification in RC3 is different between on the galactic plane and on the tangent plane of the celestial sphere. Our result also implies that there might exist biases in the luminosity functions of individual Hubble types if spiral galaxies are only classified visually.Comment: 5 pages + 8 figures, LaTe

What are S0 (0) Galaxies?

Among early-type galaxies with almost circular isophotes E0 and E1 galaxies are, at 99.3% significance, more luminous than face-on objects classified as S0 (0) and S(0) (1). This result supports the view that rotation and "diskiness" are more important in the outer regions of faint-early type galaxies than they are for more luminous galaxies of very early morphological type.Comment: 7 pages. 0 figures. Astrophysical Jounral Letters in pres

Spiral Structure and Galaxy Environment

Among 330 normal spirals of types Sa-Sc the fraction of objects exhibiting ``ring'', ``intermediate'' and ``spiral'' arm varieties does not correlated with environment. A similar conclusion appears to apply to the arm varieties of 123 barred spirals of types SBa-SBc. It is concluded that, among the northern Shapley-Ames galaxies, the distinction between the spiral and ring varieties of spiral arms is, within the accuracy of presently available data, independent of galaxy environment. This result suggests that the detailed morphology of spiral arms depends primarily on parent galaxy characteristics, rather than on the galactic environment.Comment: 8 pages. no figures. To be published in the August 2202 issue of A

The CMB Dipole and Circular Galaxy Distribution

The validity of Hubble's law defies the determination of the center of the big bang expansion, even if it exists. Every point in the expanding universe looks like the center from which the rest of the universe flies away. In this article, the author shows that the distribution of apparently circular galaxies is not uniform in the sky and that there exists a special direction in the universe in our neighborhood. The data is consistent with the assumption that the tidal force due to the mass distribution around the universe center causes the deformation of galactic shapes depending on its orientation and location relative to the center and our galaxy. Moreover, the cmb dipole data can also be associated with the center of the universe expansion, if the cmb dipole at the center of our supercluster is assumed to be due to Hubble flow. The location of the center is estimated from the cmb dipole data. The direction to the center from both sets of data is consistent and the distance to the center is computed from the cmb dipole data.Comment: 9 pages, 3 figures (10 figure captions), 1 tabl

Limitations of model fitting methods for lensing shear estimation

Gravitational lensing shear has the potential to be the most powerful tool for constraining the nature of dark energy. However, accurate measurement of galaxy shear is crucial and has been shown to be non-trivial by the Shear TEsting Programme. Here we demonstrate a fundamental limit to the accuracy achievable by model-fitting techniques, if oversimplistic models are used. We show that even if galaxies have elliptical isophotes, model-fitting methods which assume elliptical isophotes can have significant biases if they use the wrong profile. We use noise-free simulations to show that on allowing sufficient flexibility in the profile the biases can be made negligible. This is no longer the case if elliptical isophote models are used to fit galaxies made up of a bulge plus a disk, if these two components have different ellipticities. The limiting accuracy is dependent on the galaxy shape but we find the most significant biases for simple spiral-like galaxies. The implications for a given cosmic shear survey will depend on the actual distribution of galaxy morphologies in the universe, taking into account the survey selection function and the point spread function. However our results suggest that the impact on cosmic shear results from current and near future surveys may be negligible. Meanwhile, these results should encourage the development of existing approaches which are less sensitive to morphology, as well as methods which use priors on galaxy shapes learnt from deep surveys.Comment: 10 pages, 8 figure

Constraints on the Massive Supernova Progenitors

Generally accepted scheme distinguishes two main classes of supernovae (SNe): Ia resulting from the old stellar population (deflagration of a white dwarf in close binary systems), and SNe of type II and Ib/c whose ancestors are young massive stars (died in a core-collapse explosion). Concerning the latter, there are suggestions that the SNe II are connected to early B stars, and SNe Ib/c to isolated O or Wolf-Rayet (W-R) stars. However, little or no effort was made to further separate SNe Ib from Ic. We have used assumed SN rates for different SN types in spiral galaxies in an attempt to perform this task. If isolated progenitor hypothesis is correct, our analysis indicates that SNe Ib result from stars of main-sequence mass $23 \mathcal{M}_{\odot} \lesssim \mathcal{M} \lesssim 30 \mathcal{M}_{\odot}$, while the progenitors of SNe Ic are more massive stars with $\mathcal{M} \gtrsim 30 \mathcal{M}_{\odot}$. Alternatively, if the majority of SNe Ib/c appear in close binary systems (CBs) then they would result from the same progenitor population as most of the SNe II, i.e. early B stars with initial masses of order $\mathcal{M} \sim 10 \mathcal{M}_{\odot}$. Future observations of SNe at high-redshift ($z$) and their rate will provide us with unique information on SN progenitors and star-formation history of galaxies. At higher-$z$ (deeper in the cosmic past) we expect to see the lack of type Ia events, i.e. the dominance of core-collapse SNe. Better understanding of the stripped-envelope SNe (Ib/c), and their potential use as distance indicators at high-$z$, would therefore be of great practical importance.Comment: 11 pages, 2 figures, accepted for publication in IJMP