arXiv subjects

J. Schombert

Publications and source records attributed to J. Schombert.

22 records · Page 2Linked to original sources

arXiv2000

Ages and Metallicities of Fornax Dwarf Ellipticals

Narrow band photometry is presented on 27 dwarf ellipticals in the Fornax cluster. Calibrated with Galactic globular cluster data and spectrophotometric population models, the colors indicated that dwarf ellipticals have a mean [Fe/H] of -1.00+/-0.28 ranging from -1.6 to -0.4. The mean age of dwarf ellipticals, also determined photometrically, is estimated at 10+/-1 Gyrs compared to 13 Gyrs for bright Fornax ellipticals. Comparison of our metallicity color and Mg_2 indices demonstrates that the [Mg/Fe] ratio is lower in dwarf ellipticals than their more massive cousins, which is consistent with a longer duration of initial star formation to explain their younger ages. There is a increase in dwarf metallicity with distance from the Fornax cluster center where core galaxies are, on average, 0.5 dex more metal-poor than halo dwarfs. In addition, we find the halo dwarfs are younger in mean age compared to core dwarfs. One possible explanation is that the intracluster medium ram pressure strips the gas from dwarf ellipticals halting star formation (old age) and stopping enrichment (low metallicity) as they enter the core.

astro-ph↗

arXiv1999

Red, Gas Rich Low Surface Brightness Galaxies And Enigmatic Deviations from the Tully-Fisher Relation

[Abridged] Using the refurbished 305m Arecibo Gregorian Telescope, we detected 43 low surface brightness (LSB) galaxies from the catalog of O'Neil, Bothun, & Cornell (1997a). The detected galaxies range from 22.0 mag/arcsec^2 < mu_B(0) < 25.0 mag/arcsec^2, with colors ranging from the blue through the first detection of a very red LSB galaxies (B-V = -0.7 to 1.7). The M_HI/L_B of these galaxies ranges from 0.1 Msol/Lsol -- 50 Msol/Lsol, showing this sample to range from very gas poor to possibly the most gas rich galaxies ever detected. One of the more intriguing results of this survey is that the galaxies with the highest M_HI/L_B correspond to some of the reddest (optically) galaxies in the survey, raising the question of why star formation has not continued in these galaxies. Since the average H I column density in these systems is above the threshold for massive star formation, the lack of such may indicate that these galaxies form some kind of ``optical core'' which trace a much more extended distribution of neutral hydrogen. A subset of the detected LSB galaxies have rotational velocities > 200 km s^{-1} and yet are at least an order of magnitude below L* in total luminosity. As such, they represent extreme departure from the standard Tully-Fisher relation. In fact, our sample does not appear to have any significant correlation between the velocity widths and absolute magnitudes, with only 40% of the galaxies falling within the 1 sigma low surface brightness galaxy Tully-Fisher relation.

astro-ph↗

arXiv1999

Starburst Galaxies in Clusters

The nature of the starburst phenomenon in galaxies is investigated using a narrow band color system designed to study color evolution in distant clusters. Work on zero redshift, luminous far-IR galaxies, calibrated by starburst models, demonstrates the usefulness of this color system in isolating starburst from normal star-forming colors, and also demonstrates a strong correlation with far-IR colors despite reddening effects. The same color system applied to distant clusters finds that a majority of the faint blue cluster population are starburst dwarf galaxies, probably the progenitor of the current population of dwarf ellipticals in nearby clusters.

astro-ph↗

arXiv1998

The Effects of Starburst Activity on Low Surface Brightness Disk Galaxies

Although numerous simulations have been done to understand the effects of intense bursts of star formation on high surface brightness galaxies, few attempts have been made to understand how localized starbursts would affect both the color and surface brightness of low surface brightness (LSB) galaxies. To remedy this, we have run 53 simulations involving bursts of star formation activity on LSB galaxies, varying both the underlying galaxy properties and the parameters describing the starbursts. We discovered that although changing the total color of a galaxy was fairly straightforward, it was virtually impossible to alter a galaxy's central surface brightness and thereby remove it from the LSB galaxy classification without placing a high (and fairly artificial) threshold for the underlying gas density. The primary effect of large amounts of induced star formation was to produce a centralized core (bulge) component which is generally not observed in LSB galaxies. The noisy morphological appearance of LSB galaxies as well as their noisy surface brightness profiles can be reproduced by considering small bursts of star formation that are localized within the disk. The trigger mechanism for such bursts is likely distant/weak tidal encounters. The stability of disk central surface brightness to these periods of star formation argues that the large space density of LSB galaxies at z = 0 should hold to substantially higher redshifts.

astro-ph↗