19 research outputs found
The H-alpha Luminosity Function and Star Formation Rate Volume Density at z=0.8 from the NEWFIRM H-alpha Survey
[Abridged] We present new measurements of the H-alpha luminosity function
(LF) and SFR volume density for galaxies at z~0.8. Our analysis is based on
1.18m narrowband data from the NEWFIRM H-alpha Survey, a comprehensive
program designed to capture deep samples of intermediate redshift emission-line
galaxies using narrowband imaging in the near-infrared. The combination of
depth ( erg s cm in H-alpha at
3) and areal coverage (0.82 deg) complements other recent H-alpha
studies at similar redshifts, and enables us to minimize the impact of cosmic
variance and place robust constraints on the shape of the LF. The present
sample contains 818 NB118 excess objects, 394 of which are selected as H-alpha
emitters. Optical spectroscopy has been obtained for 62% of the NB118 excess
objects. Empirical optical broadband color classification is used to sort the
remainder of the sample. A comparison of the LFs constructed for the four
individual fields reveals significant cosmic variance, emphasizing that
multiple, widely separated observations are required. The dust-corrected LF is
well-described by a Schechter function with L*=10^{43.00\pm0.52} ergs s^{-1},
\phi*=10^{-3.20\pm0.54} Mpc^{-3}, and \alpha=-1.6\pm0.19. We compare our
H-alpha LF and SFR density to those at z<1, and find a rise in the SFR density
\propto(1+z)^{3.4}, which we attribute to significant L* evolution. Our H-alpha
SFR density of 10^{-1.00\pm0.18} M_sun yr^{-1} Mpc^{-3} is consistent with UV
and [O II] measurements at z~1. We discuss how these results compare to other
H-alpha surveys at z~0.8, and find that the different methods used to determine
survey completeness can lead to inconsistent results. This suggests that future
surveys probing fainter luminosities are needed, and more rigorous methods of
estimating the completeness should be adopted as standard procedure.Comment: 19 pages (emulate-ApJ format), 16 figures, 5 tables, published in
ApJ. Modified to match ApJ versio
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
Infrared Diagnostics for the Extended 12 micron Sample of Seyferts
We present an analysis of Spitzer IRS spectroscopy of 83 active galaxies from
the extended 12 micron sample. We find rank correlations between several
tracers of star formation which suggest that (1) the PAH feature is a reliable
tracer of star formation, (2) there is a significant contribution to the
heating of the cool dust by stars, (3) the H emission is also primarily
excited by star formation. The 55-90 vs. 20-30 spectral index plot is also a
diagnostic of the relative contribution of Starburst to AGN. We see there is a
large change in spectral index across the sample. Thus, the contribution to the
IR spectrum from the AGN and starburst components can be comparable in
magnitude but the relative contribution also varies widely across the sample.
We find rank correlations between several AGN tracers. We search for
correlations between AGN and Starburst tracers and we conclude that the AGN and
Starburst tracers are not correlated. This is consistent with our conclusion
that the relative strength of the AGN and Starburst components varies widely
across the sample. Thus, there is no simple link between AGN fueling and Black
Hole Growth and star formation in these galaxies. The distribution of Sil 10
micron and 18 micron strengths is consistent with the clumpy torus models of
Sirocky et al. We find a rank correlation between the [NeV] 14 micron line and
the 6.7 micron continuum which may be due to an extended component of hot dust.
The Sy 2s with a Hidden Broad Line Region (HBLR) have a higher ratio of AGN to
Starburst contribution to the SED than Sy 2s without an HBLR. This may
contribute to the detection of the HBLR in polarized light. The Sy 2s with an
HBLR are more similar to the Sy 1s than they are to the Sy 2s without an HBLR
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 H-alpha Luminosity Function and Star Formation Rate Volume Density at z=0.8 from the NEWFIRM H-alpha Survey
[Abridged] We present new measurements of the H-alpha luminosity function
(LF) and SFR volume density for galaxies at z~0.8. Our analysis is based on
1.18m narrowband data from the NEWFIRM H-alpha Survey, a comprehensive
program designed to capture deep samples of intermediate redshift emission-line
galaxies using narrowband imaging in the near-infrared. The combination of
depth ( erg s cm in H-alpha at
3) and areal coverage (0.82 deg) complements other recent H-alpha
studies at similar redshifts, and enables us to minimize the impact of cosmic
variance and place robust constraints on the shape of the LF. The present
sample contains 818 NB118 excess objects, 394 of which are selected as H-alpha
emitters. Optical spectroscopy has been obtained for 62% of the NB118 excess
objects. Empirical optical broadband color classification is used to sort the
remainder of the sample. A comparison of the LFs constructed for the four
individual fields reveals significant cosmic variance, emphasizing that
multiple, widely separated observations are required. The dust-corrected LF is
well-described by a Schechter function with L*=10^{43.00\pm0.52} ergs s^{-1},
\phi*=10^{-3.20\pm0.54} Mpc^{-3}, and \alpha=-1.6\pm0.19. We compare our
H-alpha LF and SFR density to those at z<1, and find a rise in the SFR density
\propto(1+z)^{3.4}, which we attribute to significant L* evolution. Our H-alpha
SFR density of 10^{-1.00\pm0.18} M_sun yr^{-1} Mpc^{-3} is consistent with UV
and [O II] measurements at z~1. We discuss how these results compare to other
H-alpha surveys at z~0.8, and find that the different methods used to determine
survey completeness can lead to inconsistent results. This suggests that future
surveys probing fainter luminosities are needed, and more rigorous methods of
estimating the completeness should be adopted as standard procedure.Comment: 19 pages (emulate-ApJ format), 16 figures, 5 tables, published in
ApJ. Modified to match ApJ versio
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