Pamela Marie Marcum

Comparing Galaxy Morphology at Ultraviolet and Optical Wavelengths

We have undertaken an imaging survey of 34 nearby galaxies in far-ultraviolet (FUV, ~1500 A) and optical (UBVRI) passbands to characterize galaxy morphology as a function of wavelength. This sample, which includes a range of classical Hubble types from elliptical to irregular, with emphasis on spirals at low inclination angle, provides a valuable database for comparison with images of high-z galaxies whose FUV light is redshifted into the optical and near-infrared bands. Ultraviolet data are from the Ultraviolet Imaging Telescope (UIT) Astro-2 mission. We present images and surface brightness profiles for each galaxy, and we discuss the wavelength dependence of morphology for different Hubble types in the context of understanding high-z objects. In general, the dominance of young stars in the FUV produces the patchy appearance of a morphological type later than that inferred from optical images. Prominent rings and circumnuclear star formation regions are clearly evident in FUV images of spirals, while bulges, bars, and old, red stellar disks are faint to invisible at these short wavelengths. However, the magnitude of the change in apparent morphology ranges from dramatic in early-type spirals with prominent optical bulges to slight in late-type spirals and irregulars, in which young stars dominate both the UV and optical emission. Starburst galaxies with centrally concentrated, symmetric bursts display an apparent E/S0 structure in the FUV, while starbursts associated with rings or mergers produce a peculiar morphology. We briefly discuss the inadequacy of the optically defined Hubble sequence in describing FUV galaxy images and estimating morphological k-corrections, and we suggest some directions for future research with this data set.

A Study of the Projected Galaxy Density around Nine Isolated Elliptical Galaxies

Using V-band imagery, we present results from a comparative density analysis of the local environments surrounding nine elliptical galaxies, with the objective of validating that these objects reside in extremely isolated environments. We have developed a technique that compares galaxy number density enhancements within well-studied clusters and loose groups with apparent clusterings of faint, predominantly uncataloged galaxies that are present in the fields of the isolated elliptical galaxy (IEG) candidates. The unique feature of this technique is the ability to combine size information of density peaks with number density values in order to place upper or lower limits on the distances of an apparent clustered structure in an IEG field. The utility of this technique is that probable physical association between an IEG and a clustered structure can be refuted without need of redshift information for the faint field sources. Of the nine IEG candidates studied, we conclude that one of the galaxies has possible membership with a loose group of Local Group density. Four other IEG candidates have environments that show density enhancements in the field that are possible loose groups with densities similar to the Leo or Dorado groups, but physical association with the IEGs is unlikely. The remaining four galaxies have environments that are confirmed to be isolated down to the detection limits that are detailed in the paper.

Extremely Isolated Early-type Galaxies in the Sloan Digital Sky Survey. I. The Sample

We describe the properties of a sample of extremely isolated early-type galaxies (IEGs) selected from the spectroscopic Sloan Digital Sky Survey. Sample galaxies are isolated from nearest neighbors more luminous than MV = ?16.5 by a minimum distance corresponding to 2.5?Mpc and 350?km?s?1 in redshift space. The candidate IEGs exhibit a number of unusual features as compared to bulge-dominated galaxies in cluster and group environments, including fainter luminosities, blue colors suggesting possible recent star formation, and smaller physical sizes. The paper is the first in a series analyzing this isolated galaxy sample.

Spatially-resolved far-UV properties of disk galaxies

The Ultraviolet Imaging Telescope (UIT) has returned the first significant sample of ultraviolet imagery of galaxies combining a large field-of-view and spatial resolution comparable to ground-based observatories. During the Astro Spacelab missions, UIT obtained spatially-resolved far-UV (λλ 1500 A) imagery of ∼35 disk galaxies. We have utilized the FUV light profiles and morphology to characterize the high-mass stellar populations in these systems. A variety of radial light profiles are found, including two systems, NGC 4214 and NGC 3310, which exhibit R1/4 profiles produced by their Population I stellar components.

The Astro-1/UIT ultraviolet galaxy Atlas

During the Astro-1 Spacelab missions, the Ultraviolet Imaging Telescope (UIT) obtained spatially-resolved far (λ∼1500 A) and mid-UV (λ∼2500 A) imagery of ∼25 nearby galaxies. The sample spans the Hubble sequence including ellipticals, disk systems and irregular galaxies. These images have a resolution of ∼3′′, a limiting surface brightness, μ1500≈25 mags arcsec−2, and cover the full angular extent of each system, many of which have angular diameters exceeding 5′. The UIT data permit determination of both global FUV properties with improved photometric precision, and detailed investigation of galaxian morphology at intermediate (spiral arms, nuclear rings), and small (star-forming complexes) scales. We are constructing datasets which combine the UV imagery obtained by UIT with associated optical (UBVRI,Hα) and near-IR (JHK) images of comparable depth and spatial resolution obtained at ground-based telescopes. Our primary goal is to provide a morphological Atlas of Galaxies extending from the far-ultraviole...

Ultraviolet morphologies of nearby barred and unbarred spiral galaxies

Deep high-resolution imaging of galaxies at high-redshift has revealed a remarkable diversity of emission structures in the restframe ultraviolet. To better understand these remote and primeval realms, it is important to compare them with UV-emitting counterparts in the local universe. As part of two Spacelab/Astro missions, the Ultraviolet Imaging Telescope (UIT) has obtained wide-field (40-arcmin), well-resolved (3 arcsec) images of ∼50 nearby galaxies in the vacuum ultraviolet. Followup groundbased imaging at UBVRI and Hα bands has been completed for most of the well-resolved galaxies. Analysis of a small subset of these galaxies has revealed strong variations in the emission morphologies as a function of restframe wavelength. In the present study, we compare the UV morphologies of barred and unbarred spiral galaxies as a function of Hubble type and absolute luminosity. Radial extents are measured relative to their visible counterparts, and characteristic UV emission structures are identified (e.g. rin...