12 research outputs found
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
Spitzer Local Volume Legacy (LVL) SEDs and Physical Properties
We present the panchromatic spectral energy distributions (SEDs) of the Local
Volume Legacy (LVL) survey which consists of 258 nearby galaxies (11 Mpc).
The wavelength coverage spans the ultraviolet to the infrared (1500
to 24 m) which is utilized to derive global physical
properties (i.e., star formation rate, stellar mass, internal extinction due to
dust.). With these data, we find color-color relationships and correlated
trends between observed and physical properties (i.e., optical magnitudes and
dust properties, optical color and specific star formation rate, and
ultraviolet-infrared color and metallicity). The SEDs are binned by different
galaxy properties to reveal how each property affects the observed shape of
these SEDs. In addition, due to the volume-limited nature of LVL, we utilize
the dwarf-dominated galaxy sample to test star formation relationships
established with higher-mass galaxy samples. We find good agreement with the
star-forming "main-sequence" relationship, but find a systematic deviation in
the infrared "main-sequence" at low luminosities. This deviation is attributed
to suppressed polycyclic aromatic hydrocarbon (PAH) formation in low
metallicity environments and/or the destruction of PAHs in more intense
radiation fields occurring near a suggested threshold in sSFR at a value of
log() 10.2.Comment: Accepted for publication in MNRAS (15 pages, 14 figures, 1 table
The Spitzer Local Volume Legacy (LVL) Global Optical Photometry
We present the global optical photometry of 246 galaxies in the Local Volume
Legacy (LVL) survey. The full volume-limited sample consists of 258 nearby (D <
11 Mpc) galaxies whose absolute B-band magnitude span a range of -9.6 < M_B <
-20.7 mag. A composite optical (UBVR) data set is constructed from observed
UBVR and SDSS ugriz imaging, where the ugriz magnitudes are transformed into
UBVR. We present photometry within three galaxy apertures defined at UV,
optical, and IR wavelengths. Flux comparisons between these apertures reveal
that the traditional optical R25 galaxy apertures do not fully encompass
extended sources. Using the larger IR apertures we find color-color
relationships where later-type spiral and irregular galaxies tend to be bluer
than earlier-type galaxies. These data provide the missing optical emission
from which future LVL studies can construct the full panchromatic
(UV-optical-IR) spectral energy distributions.Comment: Accepted for publication in MNRAS (9 pages, 5 figures, 5 tables
The Wyoming Survey for H-alpha. III. A Multi-wavelength Look at Attenuation by Dust in Galaxies out to z~0.4
We report results from the Wyoming Survey for H-alpha (WySH), a comprehensive
four-square degree survey to probe the evolution of star-forming galaxies over
the latter half of the age of the Universe. We have supplemented the H-alpha
data from WySH with infrared data from the Spitzer Wide-area Infrared
Extragalactic (SWIRE) Survey and ultraviolet data from the Galaxy Evolution
Explorer (GALEX) Deep Imaging Survey. This dataset provides a multi-wavelength
look at the evolution of the attenuation by dust, and here we compare a
traditional measure of dust attenuation (L(TIR)/L(FUV)) to a diagnostic based
on a recently-developed robust star formation rate (SFR) indicator,
[H-alpha_obs+24-micron]/H-alpha_obs. With such data over multiple epochs, the
evolution in the attenuation by dust with redshift can be assessed. We present
results from the ELAIS-N1 and Lockman Hole regions at z~0.16, 0.24, 0.32 and
0.40. While the ensemble averages of both diagnostics are relatively constant
from epoch to epoch, each epoch individually exhibits a larger attenuation by
dust for higher star formation rates. Hence, an epoch to epoch comparison at a
fixed star formation rate suggests a mild decrease in dust attenuation with
redshift.Comment: 30 pages, 9 figure