1,642 research outputs found
The spectral characteristics of the 2dFGRS-NVSS galaxies
We have analysed the 2dF spectra of a sample of galaxies common to the 2dF
galaxy redshift survey (2dFGRS, Colless 1999) and the NRAO VLA sky survey
(NVSS, Condon et al. 1998). Our sample comprises 88 galaxies selected by Sadler
et al. (1999) from 30 2dFGRS fields observed in 1998. In this paper we discuss
how this and future, much larger, samples of 2dFGRS-NVSS galaxies can be
interpreted via analysis of those galaxies with strong narrow emission lines.
Using diagnostic line ratio measurements we confirm the majority of the eyeball
classifications of Sadler et al. (1999), although many galaxies show evidence
of being `composite' galaxies - a mixture of AGN plus starburst components.Comment: 11 pages, 5 figures, accepted for publication in PAS
The A2667 Giant Arc at z=1.03: Evidence for Large-scale Shocks at High Redshift
We present the spatially resolved emission line ratio properties of a ~10^10
M_sun star-forming galaxy at redshift z=1.03. This galaxy is gravitationally
lensed as a triple-image giant arc behind the massive lensing cluster Abell
2667. The main image of the galaxy has magnification factors of 14+/-2.1 in
flux and ~ 2 by 7 in area, yielding an intrinsic spatial resolution of 115-405
pc after AO correction with OSIRIS at KECK II. The HST morphology shows a
clumpy structure and the H\alpha\ kinematics indicates a large velocity
dispersion with V_{max} sin(i)/\sigma ~ 0.73, consistent with high redshift
disk galaxies of similar masses. From the [NII]/H\alpha\ line ratios, we find
that the central 350 parsec of the galaxy is dominated by star formation. The
[NII]/H\alpha\ line ratios are higher in the outer-disk than in the central
regions. Most noticeably, we find a blue-shifted region of strong
[NII]/H\alpha\ emission in the outer disk. Applying our recent HII region and
slow-shock models, we propose that this elevated [NII]/H\alpha\ ratio region is
contaminated by a significant fraction of shock excitation due to galactic
outflows. Our analysis suggests that shocked regions may mimic flat or inverted
metallicity gradients at high redshift.Comment: 11 pages, 9 figures, ApJ accepte
The Host Galaxy of GRB 060505: Host ISM Properties
We investigate the ISM environment of GRB 060505. Using optical emission-line
diagnostic ratios, we compare the ISM properties of the GRB 060505 host region
with the hosts of unambiguous long- and short-duration GRBs. We show that the
metallicity, ionization state, and star formation rate of the GRB 060505
environment are more consistent with short-duration GRBs than with
long-duration GRBs. We compare the metallicity and star formation rates of the
GRB 060505 region with four other star-forming regions within the GRB 060505
host galaxy. We find no significant change in metallicity or star formation
rate between the GRB 060505 region and the other four host regions. Our results
are consistent with a compact-object-merger progenitor for GRB 060505.Comment: 7 pages, two figures; accepted for publication in ApJ
An Integral Field Study of Abundance Gradients in Nearby LIRGs
We present for the first time metallicity maps generated using data from the
Wide Field Spectrograph (WiFeS) on the ANU 2.3m of 9 Luminous Infrared Galaxies
(LIRGs) and discuss the abundance gradients and distribution of metals in these
systems. We have carried out optical integral field spectroscopy (IFS) of
several several LIRGs in various merger phases to investigate the merger
process. In a major merger of two spiral galaxies with preexisting disk
abundance gradients, the changing distribution of metals can be used as a
tracer of gas flows in the merging system as low metallicity gas is transported
from the outskirts of each galaxy to their nuclei. We employ this fact to probe
merger properties by using the emission lines in our IFS data to calculate the
gas-phase metallicity in each system. We create abundance maps and subsequently
derive a metallicity gradient from each map. We compare our measured gradients
to merger stage as well as several possible tracers of merger progress and
observed nuclear abundances. We discuss our work in the context of previous
abundance gradient observations and compare our results to new galaxy merger
models which trace metallicity gradient. Our results agree with the observed
flattening of metallicity gradients as a merger progresses. We compare our
results with new theoretical predictions that include chemical enrichment. Our
data show remarkable agreement with these simulations.Comment: Accepted for publication in ApJ. 26 pages, 18 figure
The Origin of [OII] in Post-Starburst and Red-Sequence Galaxies in High-Redshift Clusters
We present the first results from a near-IR spectroscopic campaign of the
Cl1604 supercluster at z~0.9 and the cluster RX J1821.6+6827 at z~0.82 to
investigate the nature of [OII] 3727A emission in cluster galaxies at high
redshift. Of the 401 members in the two systems, 131 galaxies have detectable
[OII] emission with no other signs of current star-formation, as well as strong
absorption features indicative of a well-established older stellar population.
The combination of these features suggests that the primary source of [OII]
emission in these galaxies is not the result of star-formation, but rather due
to the presence of a LINER or Seyfert component. Using the NIRSPEC spectrograph
on the Keck II 10-m telescope, 19 such galaxies were targeted, as well as six
additional [OII]-emitting cluster members that exhibited other signs of ongoing
star-formation. Nearly half (~47%) of the 19 [OII]-emitting, absorption-line
dominated galaxies exhibit [OII] to Ha equivalent width ratios higher than
unity, the typical value for star-forming galaxies. A majority (~68%) of these
19 galaxies are classified as LINER/Seyfert based on the emission-line ratio of
[NII] and Ha, increasing to ~85% for red [OII]-emitting, absorption-line
dominated galaxies. The LINER/Seyfert galaxies exhibit L([OII])/L(Ha) ratios
significantly higher than that observed in populations of star-forming
galaxies, suggesting that [OII] is a poor indicator of star-formation in a
large fraction of high-redshift cluster members. We estimate that at least ~20%
of galaxies in high-redshift clusters contain a LINER/Seyfert component that
can be revealed with line ratios. We also investigate the effect this
population has on the star formation rate of cluster galaxies and the
post-starburst fraction, concluding that LINER/Seyferts must be accounted for
if these quantities are to be meaningful.Comment: 33 pages, 17 figures, to appear in Ap
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