Possible Local Spiral Counterparts to Compact Blue Galaxies at Intermediate Redshift

We identify nearby disk galaxies with optical structural parameters similar to those of intermediate-redshift compact blue galaxies. By comparing HI and optical emission-line widths, we show that the optical widths substantially underestimate the true kinematic widths of the local galaxies. By analogy, optical emission-line widths may underrepresent the masses of intermediate-z compact objects. For the nearby galaxies, the compact blue morphology is the result of tidally-triggered central star formation: we argue that interactions and minor mergers may cause apparently compact morphology at higher redshift.Comment: 5 pages, uses emulateapj5 and psfig. To appear in ApJ

Angular Sizes of Faint Field Disk Galaxies: Intrinsic Luminosity Evolution

In order to explain the small scale-lengths detected in the recent deep field observations performed from large ground-based telescopes and from the Hubble Space Telescope, we investigate the predictions at high redshifts for disk galaxies that formed by infall. Changes with redshift in the observed properties of field galaxies are directly related to the evolution of the disks and of the stellar populations. We see that changes in the rest frame luminosity of a galaxy induce smaller values of half-light radii than are predicted assuming no evolution. Comparisons are presented with two observed samples from Mutz et al. (1994) and Smail et al. (1995).Comment: plain tex file + 3 postscript figures. To be published in ApJ

Retrieving Bulge and Disk Parameters and Asymptotic Magnitudes from the Growth Curves of Galaxies

We show that the growth curves of galaxies can be used to determine their bulge and disk parameters and bulge-to-total luminosity ratios, in addition to their conventional asymptotic magnitudes, provided that the point spread function is accurately known and signal-to-noise ratio is modest (S/N$\gtrsim30$). The growth curve is a fundamental quantity that most future large galaxy imaging surveys will measure. Bulge and disk parameters retrieved from the growth curve will enable us to perform statistical studies of luminosity structure for a large number of galaxies.Comment: 28 pages including 13 PS figures; accepted for publication in PAS

CO-bandhead spectroscopy of IC 342: mass and age of the nuclear star cluster

We have used the NASA Infra-Red Telescope Facility (IRTF) to observe the nuclear stellar cluster in the nearby, face-on, giant Scd spiral IC 342. From high resolution (R = 21500) spectra at the 12CO (2-0) bandhead at 2.3 micron we derive a line-of-sight stellar velocity dispersion sigma = (33 +- 3) km/s. To interpret this observation we construct dynamical models based on the Jeans equation for a spherical system. The light distribution of the cluster is modeled using an isophotal analysis of an HST V-band image from the HST Data Archive, combined with new ground-based K-band imaging. Under the assumption of an isotropic velocity distribution, the observed kinematics imply a K-band mass-to-light ratio M/L_K = 0.05, and a cluster mass M ~ 6 times 10^6 Msun. We model the mass-to-light ratio with the `starburst99' stellar population synthesis models of Leitherer and collaborators, and infer a best-fitting cluster age in the range 63-630 Myears. Although this result depends somewhat on a number of uncertainties in the modeling (e.g., the assumed extinction along the line-of-sight towards the nucleus, the IMF of the stellar population model, and the velocity dispersion anisotropy of the cluster), none of these can be plausibly modified to yield a significantly larger age. We discuss the implications of this result on possible scenarios for the frequency of nuclear starbursts and their impact on secular evolution of spiral galaxy nuclei. As a byproduct of our analysis, we infer that IC 342 cannot have any central black hole more massive than 0.5 million solar masses. This is ~ 6 times less massive than the black hole inferred to exist in our Galaxy, consistent with the accumulating evidence that galaxies with less massive bulges harbor less massive black holes.Comment: 27 pages, incl. 9 figures, submitted to The Astronomical Journa

A near infrared photometric plane for ellipticals and bulges of spirals

We report the existence of a single plane in the space of global photometric parameters describing elliptical galaxies and the bulges of early type spiral galaxies. The three parameters which define the plane are obtained by fitting the Sersic form to the brightness distribution obtained from near-infrared K band images. We find, from the range covered by their shape parameters, that the elliptical galaxies form a more homogeneous population than the bulges. Known correlations like the Kormendy relation are projections of the photometric plane. The existence of the plane has interesting implications for bulge formation models.Comment: 12 pages, LaTeX including 5 figures. To appear in the Astrophysical Journal Letter

Galactic bulges from Hubble Space Telescope NICMOS observations: the lack of r^{1/4} bulges

We use HST near-infrared imaging to explore the shapes of the surface brightness profiles of bulges of S0-Sbc galaxies at high resolution. Modeling extends to the outer bulge via bulge-disk decompositions of combined HST - ground based profiles. Compact, central unresolved components similar to those reported by others are found in ~84% of the sample. We also detect a moderate frequency (~34%) of nuclear components with exponential profiles which may be disks or bars. Adopting the S\'ersic r^{1/n} functional form for the bulge, none of the bulges have an r^{1/4} behaviour; derived S\'ersic shape-indices are = 1.7 \pm 0.7. For the same sample, fits to NIR ground-based profiles yield S\'ersic indices up to n = 4-6. The high-$n$ of ground-based profiles are a result of nuclear point sources blending with the bulge extended light due to seeing. The low S\'ersic indices are not expected from merger violent relaxation, and argue against significant merger growth for most bulges.Comment: 4 pages, 3 figures, accepted for the Astrophysical Journal Letter

Two dimensional bulge disk decomposition

We propose a two dimensional galaxy fitting algorithm to extract parameters of the bulge, disk, and a central point source from broad band images of galaxies. We use a set of realistic galaxy parameters to construct a large number of model galaxy images which we then use as input to our galaxy fitting program to test it. We find that our approach recovers all structural parameters to a fair degree of accuracy. We elucidate our procedures by extracting parameters for 3 real galaxies -- NGC 661, NGC 1381, and NGC 1427.Comment: 23 pages, LaTeX, AASTEX macros used, 7 Postscript figures, submitted to Ap

The Galaxy Populations of X-Ray Detected, Poor Groups

(Abridged) We determine the quantitative morphology and star formation properties of galaxies in six nearby X-ray detected, poor groups using multi-object spectroscopy and wide-field R imaging. We measure structural parameters for each galaxy by fitting a PSF-convolved, two component model to their surface brightness profiles. To compare directly the samples, we fade, smooth, and rebin each galaxy image so that we effectively observe each galaxy at the same redshift (9000 km/s) and physical resolution (0.87h^(-1) kpc). We compare results for the groups to a sample of field galaxies. We find that: 1) Galaxies spanning a wide range in morphological type and luminosity are well-fit by a de Vaucouleurs bulge with exponential disk profile. 2) Morphologically classifying these nearby group galaxies by their bulge fraction (B/T) is fairly robust on average, even when their redshift has increased by up to a factor of four and the effective resolution of the images is degraded by up to a factor of five. 3) The fraction of bulge-dominated systems in these groups is higher than in the field (~50% vs. ~20%). 4) The fraction of bulge-dominated systems in groups decreases with increasing radius, similar to the morphology-radius (~density) relation observed in galaxy clusters. 5) Current star formation in group galaxies is correlated with significant morphological asymmetry for disk-dominated systems (B/T<0.4). 6) The group galaxies that are most disk-dominated (B/T<0.2) are less star forming and asymmetric on average than their counterparts in the field.Comment: Accepted for publication in the Astrophysical Journal (26 pages + 12 figures); Figs 1 & 2 also available at http://www.ucolick.org/~vy/astronomy/groups_figs.tar.g

Low-Surface-Brightness Galaxies in the Sloan Digital Sky Survey. I. Search Method and Test Sample

In this paper we present results of a pilot study to use imaging data from the Sloan Digital Sky Survey (SDSS) to search for low-surface-brightness (LSB) galaxies. For our pilot study we use a test sample of 92 galaxies from the catalog of Impey et al. (1996) distributed over 93 SDSS fields of the Early Data Release (EDR). Many galaxies from the test sample are either LSB or dwarf galaxies. To deal with the SDSS data most effectively a new photometry software was created, which is described in this paper. We present the results of the selection algorithms applied to these 93 EDR fields. Two galaxies from the Impey et al. test sample are very likely artifacts, as confirmed by follow-up imaging. With our algorithms, we were able to recover 87 of the 90 remaining test sample galaxies, implying a detection rate of $\sim$96.5%. The three missed galaxies fall too close to very bright stars or galaxies. In addition, 42 new galaxies with parameters similar to the test sample objects were found in these EDR fields (i.e., $\sim$47% additional galaxies). We present the main photometric parameters of all identified galaxies and carry out first statistical comparisons. We tested the quality of our photometry by comparing the magnitudes for our test sample galaxies and other bright galaxies with values from the literature. All these tests yielded consistent results. We briefly discuss a few unusual galaxies found in our pilot study, including an LSB galaxy with a two-component disk and ten new giant LSB galaxies.Comment: 36 pages, 16 figures, accepted for publication by AJ, some figures were bitmapped to reduce the siz