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Register a new userResolved H I observations of local analogs to z ~ 1 luminous compact blue galaxies: evidence for rotation-supported disks
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While bright, blue, compact galaxies are common at $rm z sim 1$, they are relatively rare in the local universe, and their evolutionary paths are uncertain. We have obtained resolved H I observations of nine $rm z sim 0$ luminous compact blue galaxies (LCBGs) using the Giant Metrewave Radio Telescope and Very Large Array in order to measure their kinematic and dynamical properties and better constrain their evolutionary possibilities. We find that the LCBGs in our sample are rotating galaxies that tend to have nearby companions, relatively high central velocity dispersions, and can have disturbed velocity fields. We calculate rotation velocities for each galaxy by measuring half of the velocity gradient along their major axes and correcting for inclination using axis ratios derived from SDSS images of each galaxy. We compare our measurements to those previously made with single dishes and find that single dish measurements tend to overestimate LCBGs rotation velocities and H I masses. We also compare the ratio of LCBGs rotation velocities and velocity dispersions to those of other types of galaxies and find that LCBGs are strongly rotationally supported at large radii, similar to other disk galaxies, though within their half-light radii the $rm V_{rot}/ sigma$ values of their H I are comparable to stellar $rm V_{rot}/ sigma$ values of dwarf elliptical galaxies. We find that LCBGs disks on average are gravitationally stable, though conditions may be conducive to local gravitational instabilities at the largest radii. Such instabilities could lead to the formation of star-forming gas clumps in the disk, resulting eventually in a small central bulge or bar.
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Luminous Compact Blue Galaxies (LCBGs) are compact, star-forming galaxies that are rarely observed in the local universe but abundant at z=1. This increase in LCBG number density over cosmic lookback time roughly follows the increase in the star formation rate density of the universe over the same period. We use publicly available data in the COSMOS field to study the evolution of the largest homogeneous sample of LCBGs to date by deriving their luminosity function in four redshift bins over the range $0.1leq~zleq1$. We find that over this redshift range, the characteristic luminosity (M$^{*}$) increases by $sim$0.2 mag, and the number density increases by a factor of four. While LCBGs make up only about $18%$ of galaxies more luminous than M$_{B}=-$18.5 at $zsim0.2$, they constitute roughly $54%$ at z$sim$0.9. The strong evolution in number density indicates that LCBGs are an important population of galaxies to study in order to better understand the decrease in the star formation rate density of the universe since $zsim1$.
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.
Luminous compact blue galaxies (LCBGs) are a diverse class of galaxies characterized by high luminosity, blue color, and high surface brightness that sit at the critical juncture of galaxies evolving from the blue to the red sequence. As part of our multi-wavelength survey of local LCBGs, we have been studying the HI content of these galaxies using both single-dish telescopes and interferometers. Our goals are to determine if single-dish HI observations represent a true measure of the dynamical mass of LCBGs and to look for signatures of recent interactions that may be triggering star formation in LCBGs. Our data show that while some LCBGs are undergoing interactions, many appear isolated. While all LCBGs contain HI and show signatures of rotation, the population does not lie on the Tully-Fisher relation nor can it evolve onto it. Furthermore, the HI maps of many LCBGs show signatures of dynamically hot components, suggesting that we are seeing the formation of a thick disk or spheroid in at least some LCBGs. There is good agreement between the HI and H-alpha kinematics for LCBGs, and both are similar in appearance to the H-alpha kinematics of high redshift star-forming galaxies. Our combined data suggest that star formation in LCBGs is primarily quenched by virial heating, consistent with model predictions.
We use the KPNO International Spectroscopic Survey (KISS) for emission-line galaxies to identify and describe a sample of local analogues to the luminous compact blue galaxies (LCBGs) that are observed to be abundant at intermediate and high redshift. The sample is selected using criteria believed effective at isolating true examples of LCBGs: SB_e(B-band) < 21.0 mag/arcsec^2, M(B) < -18.5 (for H_o = 75 km/s/Mpc), and B-V < 0.6. Additionally, all LCBG candidates presented are selected to have star-formation as their dominant form of activity. We examine the properties of our LCBGs and compare them to those of other KISS star-forming galaxies of the same absolute magnitude range. We find that the KISS LCBGs lie on the extreme end of a fairly continuous distribution of ``normal star-forming galaxies in the plane of surface brightness versus color. This result differs from the results of previous studies that show LCBGs at higher-z to be more separate from the ``normal (usually non-active) galaxies they are compared against. On average, LCBGs have a higher tendency to emit detectable flux in the radio continuum, have higher H-alpha luminosities by a factor of 1.6, indicating strong star-formation activity, and have slightly lower than expected metal abundances based on the luminosity-metallicity relation for KISS galaxies. We calculate the volume density of our low-z (z<0.045) sample to be 5.4 x 10^-4 h_75^3 Mpc^-3, approximately 4 times lower than the volume density of the LCBGs at 0.4 < z < 0.7 and ~10 times lower than the volume density of the population at 0.7 < z < 1.0.
The kinematic properties of the ionized gas of local Luminous Compact Blue Galaxy (LCBG) NGC 7673 are presented using three dimensional data taken with the PPAK integral field unit at the 3.5-m telescope in the Centro Astronomico Hispano Aleman. Our data reveal an asymmetric rotating velocity field with a peak to peak difference of 60 km s$^{-1}$. The kinematic centre is found to be at the position of a central velocity width maximum ($sigma=54pm1$ km s$^{-1}$), which is consistent with the position of the luminosity-weighted centroid of the entire galaxy. The position angle of the minor rotation axis is 168$^{circ}$ as measured from the orientation of the velocity field contours. At least two decoupled kinematic components are found. The first one is compact and coincides with the position of the second most active star formation region (clump B). The second one is extended and does not have a clear optical counterpart. No evidence of active galactic nuclei activity or supernovae galactic winds powering any of these two components has been found. Our data, however, show evidence in support of a previously proposed minor merger scenario in which a dwarf galaxy, tentatively identified with clump B, is falling into NGC 7673. and triggers the starburst. Finally, it is shown that the dynamical mass of this galaxy may be severely underestimated when using the derived rotation curve or the integrated velocity width, under the assumption of virialization.
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