13 research outputs found
Nearby Clumpy, Gas Rich, Star Forming Galaxies: Local Analogs of High Redshift Clumpy Galaxies
Luminous compact blue galaxies (LCBGs) have enhanced star formation rates and
compact morphologies. We combine Sloan Digital Sky Survey data with HI data of
29 LCBGs at redshift z~0 to understand their nature. We find that local LCBGs
have high atomic gas fractions (~50%) and star formation rates per stellar mass
consistent with some high redshift star forming galaxies. Many local LCBGs also
have clumpy morphologies, with clumps distributed across their disks. Although
rare, these galaxies appear to be similar to the clumpy star forming galaxies
commonly observed at z~1-3. Local LCBGs separate into three groups: 1.
Interacting galaxies (~20%); 2. Clumpy spirals (~40%); 3. Non-clumpy,
non-spirals with regular shapes and smaller effective radii and stellar masses
(~40%). It seems that the method of building up a high gas fraction, which then
triggers star formation, is not the same for all local LCBGs. This may lead to
a dichotomy in galaxy characteristics. We consider possible gas delivery
scenarios and suggest that clumpy spirals, preferentially located in clusters
and with companions, are smoothly accreting gas from tidally disrupted
companions and/or intracluster gas enriched by stripped satellites. Conversely,
as non-clumpy galaxies are preferentially located in the field and tend to be
isolated, we suggest clumpy, cold streams, which destroy galaxy disks and
prevent clump formation, as a likely gas delivery mechanism for these systems.
Other possibilities include smooth cold streams, a series of minor mergers, or
major interactions.Comment: 22 pages, 5 figure
The Evolution of Luminous Compact Blue Galaxies: Disks or Spheroids?
Luminous compact blue galaxies (LCBGs) are a diverse class of galaxies
characterized by high luminosities, blue colors, and high surface brightnesses.
Residing at the high luminosity, high mass end of the blue sequence, LCBGs sit
at the critical juncture of galaxies that are evolving from the blue to the red
sequence. Yet we do not understand what drives the evolution of LCBGs, nor how
they will evolve. Based on single-dish HI observations, we know that they have
a diverse range of properties. LCBGs are HI-rich with M(HI)=10^{9-10.5} M(sun),
have moderate M(dyn)=10^{10-12} M(sun), and 80% have gas depletion timescales
less than 3 Gyr. These properties are consistent with LCBGs evolving into
low-mass spirals or high mass dwarf ellipticals or dwarf irregulars. However,
LCBGs do not follow the Tully-Fisher relation, nor can most evolve onto it,
implying that many LCBGs are not smoothly rotating, virialized systems. GMRT
and VLA HI maps confirm this conclusion revealing signatures of recent
interactions and dynamically hot components in some local LCBGs, consistent
with the formation of a thick disk or spheroid. Such signatures and the high
incidence of close companions around LCBGs suggest that star formation in local
LCBGs is likely triggered by interactions. The dynamical masses and apparent
spheroid formation in LCBGs combined with previous results from optical
spectroscopy are consistent with virial heating being the primary mechanism for
quenching star formation in these galaxies.Comment: 4 pages, 1 figure, to appear in "Hunting for the Dark: The Hidden
Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista &
C.C. Popescu, AIP Conf. Se
Light Curves and Period Changes of Type II Cepheids in the Globular Clusters M3 and M5
Light curves in the B, V, and I_c passbands have been obtained for the type
II Cepheids V154 in M3 and V42 and V84 in M5. Alternating cycle behavior,
similar to that seen among RV Tauri variables, is confirmed for V84. Old and
new observations, spanning more than a century, show that V154 has increased in
period while V42 has decreased in period. V84, on the other hand, has shown
large, erratic changes in period that do not appear to reflect the long term
evolution of V84 through the HR diagram.Comment: 28 pages, 12 figure
Light curves and period changes of type II cepheids in the globular clusters M3 and M5
Light curves in the B, V, and Ic passbands have been obtained for the type II Cepheids V154 in M3 and V42 and V84 in M5. Alternating cycle behavior, similar to that seen among RV Tauri variables, is confirmed for V84. Old and new observations, spanning more than a century, show that V154 has increased in period while V42 has decreased in period. V84, on the other hand, has shown large, erratic changes in period that do not appear to reflect the long-term evolution of V84 through the Hertzsprung-Russel diagram