A Look At Three Different Scenarios for Bulge Formation

In this paper, we present three qualitatively different scenarios for bulge formation: a secular evolution model in which bulges form after disks and undergo several central starbursts, a primordial collapse model in which bulges and disks form simultaneously, and an early bulge formation model in which bulges form prior to disks. We normalize our models to the local z=0 observations of de Jong & van der Kruit (1994) and Peletier & Balcells (1996) and make comparisons with high redshift observations. We consider model predictions relating directly to bulge-to-disk properties. As expected, smaller bulge-to-disk ratios and bluer bulge colors are predicted by the secular evolution model at all redshifts, although uncertainties in the data are currently too large to differentiate strongly between the models.Comment: 19 pages, 6 figures, accepted for publication in the Astrophysical Journa

Search for the magnetic field of the O7.5 III star xi Persei

Cyclical wind variability is an ubiquitous but as yet unexplained feature among OB stars. The O7.5 III(n)((f)) star xi Persei is the brightest representative of this class on the Northern hemisphere. As its prominent cyclical wind properties vary on a rotational time scale (2 or 4 days) the star has been already for a long time a serious magnetic candidate. As the cause of this enigmatic behavior non-radial pulsations and/or a surface magnetic field are suggested. We present a preliminary report on our attempts to detect a magnetic field in this star with high-resolution measurements obtained with the spectropolarimeter Narval at TBL, France during 2 observing runs of 5 nights in 2006 and 5 nights in 2007. Only upper limits could be obtained, even with the longest possible exposure times. If the star hosts a magnetic field, its surface strength should be less than about 300 G. This would still be enough to disturb the stellar wind significantly. From our new data it seems that the amplitude of the known non-radial pulsations has changed within less than a year, which needs further investigation.Comment: 2 pages, 6 figures, contributed poster at IAU Symposium 259 "Cosmic Magnetic Fields: from Planets, to Stars and Galaxies", Tenerife, Spain, November 3-7, 200

Dark and Baryonic Matter in Bright Spiral Galaxies: I.Near-infrared and Optical Broadband Surface Photometry of 30 Galaxies

We present photometrically calibrated images and surface photometry in the B, V, R, J, H, and K-bands of 25, and in the g, r, and K-bands of 5 nearby bright (Bo_T<12.5 mag) spiral galaxies with inclinations between 30-65 degrees spanning the Hubble Sequence from Sa to Scd. Data are from The Ohio State University Bright Spiral Galaxy Survey, the Two Micron All Sky Survey, and the Sloan Digital Sky Survey Second Data Release. Radial surface brightness profiles are extracted, and integrated magnitudes are measured from the profiles. Axis ratios, position angles, and scale lengths are measured from the near-infrared images. A 1-dimensional bulge/disk decomposition is performed on the near-infrared images of galaxies with a non-negligible bulge component, and an exponential disk is fit to the radial surface brightness profiles of the remaining galaxies.Comment: 28 page

A new catalog of photometric redshifts in the Hubble Deep Field

Using the newly available infrared images of the Hubble Deep Field in the J, H, and K bands and an optimal photometric method, we have refined a technique to estimate the redshifts of 1067 galaxies. A detailed comparison of our results with the spectroscopic redshifts in those cases where the latter are available shows that this technique gives very good results for bright enough objects (AB(8140) < 26.0). From a study of the distribution of residuals (Dz(rms)/(1+z) ~ 0.1 at all redshifts) we conclude that the observed errors are mainly due to cosmic variance. This very important result allows for the assessment of errors in quantities to be directly or indirectly measured from the catalog. We present some of the statistical properties of the ensemble of galaxies in the catalog, and finish by presenting a list of bright high-redshift (z ~ 5) candidates extracted from our catalog, together with recent spectroscopic redshift determinations confirming that two of them are at z=5.34 and z=5.60.Comment: 28 pages, 12PS+4JPEG figures, aaspp style. Accepted for publication in The Astrophysical Journal. The catalog, together with a clickable map of the HDF, Tables 4 and 5 (HTML, LaTeX or ASCII format), and the figures, are available at http://bat.phys.unsw.edu.au/~fsoto/hdfcat.htm

The Way We Measure: Comparison of Methods to Derive Radial Surface Brightness Profiles

The breaks and truncations in the luminosity profile of face-on spiral galaxies offer valuable insights in their formation history. The traditional method of deriving the surface photometry profile for face-on galaxies is to use elliptical averaging. In this paper, we explore the question whether elliptical averaging is the best way to do this. We apply two additional surface photometry methods, one new: principle axis summation, and one old that has become seldom used: equivalent profiles. These are compared to elliptically averaged profiles using a set of 29 face-on galaxies. We find that the equivalent profiles match extremely well with elliptically averaged profiles, confirming the validity of using elliptical averaging. The principle axis summation offers a better comparison to edge-on galaxies.Comment: Accepted for publication by Monthly Notices of the R.A.S. A hi-res version is available at http://www.astro.rug.nl/~vdkruit/Petersetal-VI.pd

Models of Disk Evolution: Confrontation with Observations

We present simple models for disk evolution based on two different approaches: a forward approach based on predictions generic to hierarchical models for structure formation (e.g., Mo, Mao, & White 1998) and a backwards approach based on detailed modeling of the Milky Way galaxy (e.g., Bouwens, Cayon, & Silk 1997). We normalize these models to local observations and predict high-redshift luminosities, sizes, circular velocities, and surface brightnesses. Both approaches yield somewhat similar predictions for size, surface brightness, and luminosity evolution though they clearly differ in the amount of number evolution. These predictions seem to be broadly consistent with the high-redshift observations of Simard et al. (1999), suggesting that the B-band surface brightness of disks has indeed evolved by ~1.5 mag from z~0 to z~1 similar to the models and is not an artifact of selection effects as previously claimed. We also find a lack of low surface brightness galaxies in several high redshift samples relative to model predictions based on local samples (de Jong & van der Kruit 1994; Mathewson, Ford, & Buchhorn 1992).Comment: 34 pages, 9 figures, accepted to Ap

New and Old Tests of Cosmological Models and Evolution of Galaxies

We describe the classical cosmological tests, such as the Log$N$-Log$S$, redshift-magnitude and angular diameter tests, and propose some new tests of the evolution of galaxies and the universe. Most analyses of these tests treat the problem in terms of a luminosity function and its evolution which can lead to incorrect conclusions when dealing with high redshift sources. We develop a proper treatment in three parts. In the first part we describe these tests based on the isophotal values of the quantities such as flux, size or surface brightness. We show the shortcomings of the simple point source approximation based solely on the luminosity function and consideration of the flux limit. We emphasize the multivariate nature of the problem and quantify the effects of other selection biases due to the surface brightness and angular size limitations. In these considerations the surface brightness profile plays a critical role. In the second part we show that considerable simplification over the complicated isophotal scheme is achieved if these test are carried out in some sort of metric scheme, for example that suggested by Petrosian (1976). This scheme, however, is limited to well resolved sources. Finally, we describe the new tests, which use the data to a fuller extent than the isophotal or metric based tests, and amount to simply counting the pixels or adding their intensities as a function of the pixel surface brightness, instead of dealing with surface brightness, sizes and fluxes of individual galaxies. We show that the data analysis and its comparison with the theoretical models of the distributions and evolution of galaxies has the simplicity of the metric test and utilizes the data more fully than the isophotal test.Comment: 29 pages including 8 figures. http://www-bigbang.stanford.edu/~vahe/papers/finals/newtest.ps. To appear in ApJ, Oct. 199