Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userThe Nature of Nearby Counterparts to Intermediate-Redshift Luminous Compact Blue Galaxies. III. Interferometric Observations of Neutral Atomic and Molecular Gas
136
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
We present the results of a VLA and OVRO-MMA follow-up to our single-dish surveys of the neutral atomic and molecular gas in a sample of nearby Luminous Compact Blue Galaxies (LCBGs). These luminous, blue, high surface brightness, starbursting galaxies were selected using criteria similar to that used to define LCBGs at higher redshifts. The surveys were undertaken to study the nature and evolutionary possibilities of LCBGs, using dynamical masses and gas depletion time scales as constraints. Here we present nearly resolved VLA H I maps of four LCBGs, as well as results from the literature for a fifth LCBG. In addition, we present OVRO-MMA maps of CO(J=1-0) in two of these LCBGs. We have used the resolved H I maps to separate the H I emission from target galaxies and their companions to improve the accuracy of our gas and dynamical mass estimates. For this sub-sample of LCBGs, we find that the dynamical masses measured with the single-dish telescope and interferometer are in agreement. However, we find that we have overestimated the mass of H I in two galaxies by a significant amount, possibly as much as 75%, when compared to the single-dish estimates. These two galaxies have companions within a few arc minutes; we find that our single-dish and interferometric measurements of H I masses are in reasonable agreement for galaxies with more distant companions. The H I velocity fields indicate that all five galaxies are clearly rotating yet distorted, likely due to recent interactions. Our measurements of the gas and dynamical masses of LCBGs point towards evolution into low mass galaxies such as dwarf ellipticals, irregulars, and low mass spirals, consistent with studies of LCBGs at higher redshifts.
rate research
Read More
We present single-dish H I spectra obtained with the Green Bank Telescope, along with optical photometric properties from the Sloan Digital Sky Survey, of 20 nearby (D < 70 Mpc) Luminous Compact Blue Galaxies (LCBGs). These ~L*, blue, high surface brightness, starbursting galaxies were selected with the same criteria used to define LCBGs at higher redshifts. We find these galaxies are gas-rich, with M(HI) ranging from 5*10^8 to 8*10^9 M_sun, and M(HI)/L_B ranging from 0.2 to 2 M_sun/L_sun, consistent with a variety of morphological types of galaxies. We find the dynamical masses (measured within R_25) span a wide range, from 3*10^9 to 1*10^11 M_sun. However, at least half have dynamical mass-to-light ratios smaller than nearby galaxies of all Hubble types, as found for LCBGs at intermediate redshifts. By comparing line widths and effective radii with local galaxy populations, we find that LCBGs are consistent with the dynamical mass properties of Magellanic (low luminosity) spirals, and the more massive irregulars and dwarf ellipticals, such as NGC 205.
We identify nearby disk galaxies with optical structural parameters similar to those of intermediate-redshift compact blue galaxies. By comparing HI and optical emission-line widths, we show that the optical widths substantially underestimate the true kinematic widths of the local galaxies. By analogy, optical emission-line widths may underrepresent the masses of intermediate-z compact objects. For the nearby galaxies, the compact blue morphology is the result of tidally-triggered central star formation: we argue that interactions and minor mergers may cause apparently compact morphology at higher redshift.
We present Arecibo 21 cm spectroscopy, Keck HIRES Hb spectroscopy, and WIYN R-band images of 11 nearby blue compact galaxies selected to be similar to blue compact star-forming galaxies at intermediate redshifts (0.1<z<1). We detect HI in 10 of 11 sample galaxies, yielding HI masses of 0.3-4x10^9 M_odot, HI linewidths, W_20, of 133-249 km/s, dynamical masses of 0.5-5x10^10 M_odot, gas depletion timescales, tau_gas, of 0.3-7 Gyr, HI mass fractions of 0.01-0.58, and mass-to-light ratios of 0.1-0.8. These values span the range typical of nearby HII galaxies, irregulars and spirals. Despite the restricted morphological selection, our sample is quite heterogeneous in HI content, dynamical mass, and gas depletion timescale. Therefore, these galaxies should look very different from each other in 5 Gyr. Fading of intermediate-z luminous blue compact galaxies into NGC-type spheroidals is a viable evolutionary scenario for the least massive, most gas-poor objects. The most consistent characteristic of our sample is that the ratio, R, of HII linewidth to HI 21 cm linewidth (W_20) are systematically less than unity. The simplest explanation is that the ionized gas is more centrally concentrated than the neutral gas within the gravitational potential. On average R=0.66 +/- 0.16, similar to findings for local HII galaxies. We find R is also a function of linewidth; smaller linewidth galaxies have smaller values of R. Correcting optical linewidths by this factor raises derived masses and places these galaxies on the local luminosity--linewidth (Tully-Fisher) relation. If this ratio applies to intermediate-redshift galaxies, then the proposed luminosity evolution of the Tully-Fisher relation is much smaller and more gradual than suggested by studies using optical emission-linewidth measurements.
We present the results of high spatial resolution HI observations of five intrinsically compact dwarf galaxies which are currently experiencing a strong burst of star formation. The HI maps indicate that these systems have a complex and clumpy interstellar medium. Unlike typical dwarf irregular galaxies, these Blue Compact Dwarf (BCD) galaxies exhibit strong central concentrations in their neutral gas distributions which may provide a clue to the origin of their strong star-burst activity. Furthermore, while all of the systems do appear to be rotating, based on observed velocity gradients, the kinematics are complex. All systems have non-ordered kinematic structure at some level; some of the extended gas is not necessarily kinematically connected to the main system. The observed gas distributions and kinematics place constraints on evolutionary scenarios for BCDs. Evolutionary links between BCDs, dwarf irregulars, and dwarf ellipticals have been postulated to explain their high star formation rates and low luminosity, low metallicity nature. The BCDs appear to have higher central mass concentrations in both gas and stellar content than the dwarf irregulars, indicating that evolutionary scenarios connecting these two classes will require mass redistribution. In addition, the fact that BCDs are rotationally supported systems indicates that BCDs are unlikely to evolve into dwarf ellipticals without substantial loss of angular momentum. Thus, while such evolutionary scenarios may still be possible with the aid of mergers or tidal interactions, the isolated nature of BCDs suggests that the majority of BCDs will not fade to become objects similar to the present day dwarf ellipticals.
We present the stellar velocity dispersion measurements for 5 Luminous Compact Galaxies (LCGs) at z=0.5-0.7. These galaxies are vigorously forming stars with average SFR $sim$ 40 M$_{odot}$/yr. We find that their velocity dispersions range from $sim137 rm{km/s}$ to $260 rm{km/s}$, while their stellar masses range between $4times 10^{9}$ and $10^{11}$ M$_{odot}$. If these LCGs evolve passively after this major burst of star formation, their masses and velocity dispersions, as well as their evolved colours and luminosities are most consistent with the values characteristic of early-type spiral galaxies today.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
