arXiv subjects

J. J. Dalcanton

Publications and source records attributed to J. J. Dalcanton.

40 records · Page 3Linked to original sources

arXiv1996

The Formation of Disk Galaxies

We present a scenario for the formation of disks which explains not only the properties of normal galaxies, but the properties of the population of low surface brightness galaxies (LSBs) as well. We use a gravitationally self-consistent model for disk collapse to calculate the observable properties of disk galaxies as a function of mass and angular momentum of the initial protogalaxy. The model naturally produces smooth, asymptotically flat rotation curves, exponential surface brightness profiles over many disk scale lengths, the Tully-Fisher relation as a function of surface brightness, the observed distribution of scale lengths and surface brightnesses, and the variation of rotation curve shapes. In the model, low mass and/or high angular momentum halos naturally form low surface brightness disks. Theoretical and numerical calculations suggest galaxy halos should form with a wide range of mass and angular momenta, and thus, the disks which form within these halos should have a wide range of surface brightnesses and scale lengths. We use the formalism to calculate the expected change in the observed luminosity function (LF) and luminosity density as a function of limiting surface brightness. Current measurements of the LF may by off by factors of 2 at L*. [SHORTENED]

astro-ph↗

arXiv1996

Chain Galaxies are Edge-On Low Surface Brightness Galaxies

Deep HST WFPC2 images have revealed a population of very narrow blue galaxies which Cowie et al. (1996) have interpreted as being a new morphological class of intrinsically linear star forming galaxies at $z=0.5-3$. We show that the same population exists in large numbers at low redshifts (z=0.03) and are actually the edge-on manifestation of low surface brightness disk galaxies.

astro-ph↗

arXiv1995

THE FORMATION OF LSB GALAXIES

The formation of low surface brightness galaxies is an unavoidable prediction of any hierarchical clustering scenario. In these models, low surface brightness galaxies form at late times from small initial overdensities, and make up most of the faint end of the galaxy luminosity function. Because there are tremendous observational biases against finding low surface brightness galaxies, the observed faint end of the galaxy luminosity function may easily fall short of predictions, if hierarchical structure formation is correct. We calculate the number density and mass density in collapsed objects as a function of baryonic surface density and redshift, and show that the mass in recently formed low surface brightness galaxies can be comparable to the mass bound into ``normal'' high surface brightness galaxies. Because of their low gas surface densities, these galaxies are easily ionized by the UV background and are not expected to appear in HI surveys. Low surface brightness galaxies (LSBs) are not a special case of galaxy formation and are perhaps better viewed as a continuance of the Hubble sequence.

astro-ph↗

arXiv1994

A New Method for Finding Clusters of Galaxies at z>1

At large redshifts, a cluster or group may be too distant for the galaxies within the cluster to be detected individually. However, the light from these ``undetected'' galaxies still modulates the surface brightness of the background sky. Clusters can appear as 10"-1.5' sized fluctuations in the surface brightness of the EBL. The fluctuations have central surface brightnesses between roughly 26 and 28 mag/sqr-arcsec (in V) for clusters between z=1 and z=2, and are brighter than the fluctuations produced by background field galaxies. While such low surface brightnesses are difficult to achieve with direct high-resolution imaging, we demonstrate that they are easily reached in short exposures through smoothing the sky in very flat CCD images. For a reasonable extrapolation of the properties and space densities of clusters and groups, we find that for a wide range of cosmological assumptions there should be tens of clusters per square degree visible in the extragalactic background. The detection rate can range between 0.1 and 100 clusters per square degree, for extreme assumptions about the rate of cluster and galaxy evolution. Drift scans provide sufficient accuracy of flat-fielding to make the method discussed in this paper an efficient techinque for finding candidate high redshift clusters.

astro-ph↗