2,903 research outputs found
A Comparison of Young Star Properties with Local Galactic Environment for LEGUS/LITTLE THINGS Dwarf Irregular Galaxies
We have explored the role environmental factors play in determining characteristics of young stellar objects in nearby dwarf irregular and blue compact dwarf galaxies. Star clusters are characterized by concentrations, masses, and formation rates; OB associations by mass and mass surface density; O stars by their numbers and near-ultraviolet absolute magnitudes; and H ii regions by Hα surface brightnesses. These characteristics are compared to surrounding galactic pressure, stellar mass density, H i surface density, and star formation rate (SFR) surface density. We find no trend of cluster characteristics with environmental properties, implying that larger-scale effects are more important in determining cluster characteristics or that rapid dynamical evolution erases any memory of the initial conditions. On the other hand, the most massive OB associations are found at higher pressure and H i surface density, and there is a trend of higher H ii region Hα surface brightness with higher pressure, suggesting that a higher concentration of massive stars and gas is found preferentially in regions of higher pressure. At low pressures we find massive stars but not bound clusters and OB associations. We do not find evidence for an increase of cluster formation efficiency as a function of SFR density. However, there is an increase in the ratio of the number of clusters to the number of O stars with increasing pressure, perhaps reflecting an increase in clustering properties with SFR
A Study of Two Dwarf Irregular Galaxies with Asymmetrical Star Formation Distributions
Two dwarf irregular galaxies, DDO 187 and NGC 3738, exhibit a striking pattern of star formation: intense star formation is taking place in a large region occupying roughly half of the inner part of the optical galaxy. We use data on the H i distribution and kinematics and stellar images and colors to examine the properties of the environment in the high star formation rate (HSF) halves of the galaxies in comparison with the low star formation rate halves. We find that the pressure and gas density are higher on the HSF sides by 30%–70%. In addition we find in both galaxies that the H i velocity fields exhibit significant deviations from ordered rotation and there are large regions of high-velocity dispersion and multiple velocity components in the gas beyond the inner regions of the galaxies. The conditions in the HSF regions are likely the result of large-scale external processes affecting the internal environment of the galaxies and enabling the current star formation there
Census of the Local Universe (CLU) Narrow-Band Survey I: Galaxy Catalogs from Preliminary Fields
We present the Census of the Local Universe (CLU) narrow-band survey to
search for emission-line (\ha) galaxies. CLU-\ha~has imaged 3 of
the sky (26,470~deg) with 4 narrow-band filters that probe a distance out
to 200~Mpc. We have obtained spectroscopic follow-up for galaxy candidates in
14 preliminary fields (101.6~deg) to characterize the limits and
completeness of the survey. In these preliminary fields, CLU can identify
emission lines down to an \ha~flux limit of
~ at 90\% completeness, and recovers 83\%
(67\%) of the \ha~flux from catalogued galaxies in our search volume at the
=2.5 (=5) color excess levels. The contamination from galaxies
with no emission lines is 61\% (12\%) for =2.5 (=5). Also, in
the regions of overlap between our preliminary fields and previous
emission-line surveys, we recover the majority of the galaxies found in
previous surveys and identify an additional 300 galaxies. In total, we
find 90 galaxies with no previous distance information, several of which are
interesting objects: 7 blue compact dwarfs, 1 green pea, and a Seyfert galaxy;
we also identified a known planetary nebula. These objects show that the
CLU-\ha~survey can be a discovery machine for objects in our own Galaxy and
extreme galaxies out to intermediate redshifts. However, the majority of the
CLU-\ha~galaxies identified in this work show properties consistent with normal
star-forming galaxies. CLU-\ha~galaxies with new redshifts will be added to
existing galaxy catalogs to focus the search for the electromagnetic
counterpart to gravitational wave events.Comment: 28 pages, 22 figures, 4 tables (Accepted to ApJ
Gene therapy for B-cell lymphoma in a SCID mouse model using an immunoglobulin-regulated diphtheria toxin gene delivered by a novel adenovirus-polylysine conjugate
The connection between galaxy environment and the luminosity function slopes of star-forming regions
We present the first study of GALEX far-ultraviolet (FUV) luminosity functions of individual star-forming regions within a sample of 258 nearby galaxies spanning a large range in total stellar mass and star formation properties. We identify ∼65 000 star-forming regions (i.e. FUV sources), measure each galaxy's luminosity function, and characterize the relationships between the luminosity function slope (α) and several global galaxy properties. A final sample of 82 galaxies with reliable luminosity functions are used to define these relationships and represent the largest sample of galaxies with the largest range of galaxy properties used to study the connection between luminosity function properties and galaxy environment. We find that α correlates with global star formation properties, where galaxies with higher star formation rates and star formation rate densities (Σ_(SFR)) tend to have flatter luminosity function slopes. In addition, we find that neither stochastic sampling of the luminosity function in galaxies with low-number statistics nor the effects of blending due to distance can fully account for these trends. We hypothesize that the flatter slopes in high Σ_(SFR) galaxies is due to higher gas densities and higher star formation efficiencies which result in proportionally greater numbers of bright star-forming regions. Finally, we create a composite luminosity function composed of star-forming regions from many galaxies and find a break in the luminosity function at brighter luminosities. However, we find that this break is an artefact of varying detection limits for galaxies at different distances
Empirical ugri-UBVRc Transformations for Galaxies
We present empirical color transformations between Sloan Digital Sky Survey
ugri and Johnson-Cousins UBVRc photometry for nearby galaxies (D < 11 Mpc). We
use the Local Volume Legacy (LVL) galaxy sample where there are 90 galaxies
with overlapping observational coverage for these two filter sets. The LVL
galaxy sample consists of normal, non-starbursting galaxies. We also examine
how well the LVL galaxy colors are described by previous transformations
derived from standard calibration stars and model-based galaxy templates. We
find significant galaxy color scatter around most of the previous
transformation relationships. In addition, the previous transformations show
systematic offsets between transformed and observed galaxy colors which are
visible in observed color-color trends. The LVL-based transformations
show no systematic color offsets and reproduce the observed color-color galaxy
trends.Comment: Accepted for publication in MNRAS (9 pages, 6 figures, 4 tables
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