78 research outputs found
Metal Abundances of KISS Galaxies. VI. New Metallicity Relations for the KISS Sample of Star-Forming Galaxies
We present updated metallicity relations for the spectral database of
star-forming galaxies (SFGs) found in the KPNO International Spectroscopic
Survey (KISS). New spectral observations of emission-line galaxies (ELGs)
obtained from a variety of telescope facilities provide oxygen abundance
information. A nearly four-fold increase in the number of KISS objects with
robust metallicities relative to our previous analysis provides for an
empirical abundance calibration to compute self-consistent metallicity
estimates for all SFGs in the sample with adequate spectral data. In addition,
a sophisticated spectral energy distribution (SED) fitting routine has provided
robust calculations of stellar mass. With these new and/or improved galaxy
characteristics, we have developed luminosity-metallicity (-) relations,
mass-metallicity (-) relations, and the so-called Fundamental
Metallicity Relation (FMR) for over 1,450 galaxies from the KISS sample. This
KISS - relation is presented for the first time and demonstrates
markedly lower scatter than the KISS - relation. We find that our
relations agree reasonably well with previous publications, modulo modest
offsets due to differences in the SEL metallicity calibrations used. We
illustrate an important bias present in previous - and -
studies involving direct-method () abundances that may result in
systematically lower slopes in these relations. Our KISS FMR shows consistency
with those found in the literature, albeit with a larger scatter. This is
likely a consequence of the KISS sample being biased toward galaxies with high
levels of activity.Comment: Accepted for publication in The Astronomical Journal; 27 pages, 15
figures, 7 tables (with Appendix
Detection of an Optical Counterpart to the ALFALFA Ultra-compact High Velocity Cloud AGC 249525
We report on the detection at 98% confidence of an optical counterpart to
AGC 249525, an Ultra-Compact High Velocity Cloud (UCHVC) discovered by the
ALFALFA blind neutral hydrogen survey. UCHVCs are compact, isolated HI clouds
with properties consistent with their being nearby low-mass galaxies, but
without identified counterparts in extant optical surveys. Analysis of the
resolved stellar sources in deep - and -band imaging from the WIYN pODI
camera reveals a clustering of possible Red Giant Branch stars associated with
AGC 249525 at a distance of 1.640.45 Mpc. Matching our optical detection
with the HI synthesis map of AGC 249525 from Adams et al. (2016) shows that the
stellar overdensity is exactly coincident with the highest-density HI contour
from that study. Combining our optical photometry and the HI properties of this
object yields an absolute magnitude of , a stellar
mass between and , and an HI to stellar mass ratio between 9 and 144. This object has
stellar properties within the observed range of gas-poor Ultra-Faint Dwarfs in
the Local Group, but is gas-dominated.Comment: 9 pages, 4 figures; accepted to ApJ
Properties of the KISS Green Pea Galaxies
Green peas (GPs) are a class of extreme star-forming galaxies (SFGs) at intermediate redshifts, originally discovered via color selection using multifilter, wide-field survey imaging data. They are commonly thought of as being analogs of high-redshift Lyα-emitting galaxies. The defining characteristic of GP galaxies is a high-excitation nebular spectrum with very large equivalent width lines, leading to the recognition that GP-like galaxies can also be identified in samples of emission-line galaxies. Here we compare the properties a sample of [O iii]-selected SFGs (z = 0.29–0.41) from the KPNO International Spectroscopic Survey (KISS) with the color-selected GPs. We find that the KISS [O iii]-selected galaxies overlap with the parameter space defined by the color-selected GPs; the two samples appear to be drawn from the same population of objects. We compare the KISS GPs with the full Hα-selected KISS SFG sample (z < 0.1) and find that they are extreme systems. Many appear to be young systems at their observed look-back times (3–4 Gyr), with more than 90% of their rest-frame B-band luminosity coming from the starburst population. We compute the volume density of the KISS red (KISSR) GPs at z = 0.29–0.41 and find that they are extremely rare objects. We do not see galaxies as extreme as the KISSR GPs in the local universe, although we recognize several lower-luminosity systems at z < 0.1
Properties of the KISS Green Pea Galaxies
Green Peas are a class of extreme star-forming galaxies at intermediate
redshifts, originally discovered via color-selection using multi-filter,
wide-field survey imaging data (Cardamone et al. 2009). They are commonly
thought of as being analogs of high-redshift Ly-emitting galaxies. The
defining characteristic of Green Pea galaxies is a high-excitation nebular
spectrum with very large equivalent width lines, leading to the recognition
that Green Pea-like galaxies can also be identified in samples of emission-line
galaxies. Here we compare the properties a sample of [O III]-selected
star-forming galaxies (z = 0.29-0.41) from the KPNO International Spectroscopic
Survey (KISS) with the color-selected Green Peas. We find that the KISS [O
III]-selected galaxies overlap with the parameter space defined by the
color-selected Green Peas; the two samples appear to be drawn from the same
population of objects. We compare the KISS Green Peas with the full
H-selected KISS star-forming galaxy sample (z 0.1) and find that
they are extreme systems. Many appear to be young systems at their observed
look-back times (3-4 Gyr), with more than 90% of their rest-frame B-band
luminosity coming from the starburst population. We compute the volume density
of the KISSR Green Peas at z = 0.29-0.41 and find that they are extremely rare
objects. We don't see galaxies as extreme as the KISSR Green Peas in the local
Universe, although we recognize several lower-luminosity systems at z 0.1.Comment: 21 pages, 12 figures. Accepted for publication in the Astrophysical
Journa
Searches for Extremely Metal Poor Galaxies using ALFALFA-selected Dwarf Galaxies
We present a study of nearby dwarf galaxies selected from the ALFALFA blind
HI survey. A primary goal of the project was to utilize a non-standard
selection method with the hope of detecting previously unrecognized extremely
metal-poor (XMP) galaxies. The study was motivated by the recent discovery of
two XMP galaxies Leo P and Leoncino which were both originally found
via the ALFALFA survey. We have obtained narrowband H images for 42
dwarf systems, many of which are located in the local void in front of the
Pisces-Perseus Supercluster. Spectra for eleven of the best candidates resulted
in the determination of metal abundances for ten of the systems. None were
found to be extremely metal poor, although one system (AGC 123350) was found to
have an oxygen abundance of log(O/H)+12 = 7.46, or 6\% solar. One of the
galaxies in our sample exhibits a high oxygen abundance for its luminosity,
suggesting the possibility that it may have a tidal origin.Comment: 21 pages, 11 figures, 4 table
xGASS: Cold gas content and quenching in galaxies below the star forming main sequence
We use HI and H2 global gas measurements of galaxies from xGASS and xCOLD
GASS to investigate quenching paths of galaxies below the star formation main
sequence (SFMS). We show that the population of galaxies below the SFMS is not
a 1:1 match with the population of galaxies below the HI and H2 gas fraction
scaling relations. Some galaxies in the transition zone (TZ) 1-sigma below the
SFMS can be as HI-rich as those in the SFMS, and have on average longer gas
depletion timescales. We find evidence for environmental quenching of
satellites, but central galaxies in the TZ defy simple quenching pathways. Some
of these so-called "quenched" galaxies may still have significant gas
reservoirs and be unlikely to deplete them anytime soon. As such, a correct
model of galaxy quenching cannot be inferred with SFR (or other optical
observables) alone, but must include observations of the cold gas. We also find
that internal structure (particularly, the spatial distribution of old and
young stellar populations) plays a significant role in regulating the star
formation of gas-rich isolated TZ galaxies, suggesting the importance of bulges
in their evolution.Comment: 15 pages, 11 figures, accepted for publication in MNRA
Discovery of a Gas-Rich Companion to the Extremely Metal-Poor Galaxy DDO 68
We present HI spectral-line imaging of the extremely metal-poor galaxy DDO
68. This system has a nebular oxygen abundance of only 3% Z, making
it one of the most metal-deficient galaxies known in the local volume.
Surprisingly, DDO 68 is a relatively massive and luminous galaxy for its metal
content, making it a significant outlier in the mass-metallicity and
luminosity-metallicity relationships. The origin of such a low oxygen abundance
in DDO 68 presents a challenge for models of the chemical evolution of
galaxies. One possible solution to this problem is the infall of pristine
neutral gas, potentially initiated during a gravitational interaction. Using
archival HI spectral-line imaging obtained with the Karl G. Jansky Very Large
Array, we have discovered a previously unknown companion of DDO 68. This
low-mass (M 2.810 M), recently
star-forming (SFR 1.410 M yr,
SFR 710 M yr) companion has
the same systemic velocity as DDO 68 (V 506 km s; D
12.740.27 Mpc) and is located at a projected distance of 42 kpc. New HI
maps obtained with the 100m Robert C. Byrd Green Bank Telescope provide
evidence that DDO 68 and this companion are gravitationally interacting at the
present time. Low surface brightness HI gas forms a bridge between these
objects.Comment: Accepted for publication in the Astrophysical Journal Letter
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