1,337 research outputs found
The Mass-Metallicity and Luminosity-Metallicity Relation from DEEP2 at z ~ 0.8
We present the mass-metallicity (MZ) and luminosity-metallicity (LZ)
relations at z ~ 0.8 from ~1350 galaxies in the Deep Extragalactic Evolutionary
Probe 2 (DEEP2) survey. We determine stellar masses by fitting the spectral
energy distribution inferred from photometry with current stellar population
synthesis models. This work raises the number of galaxies with metallicities at
z ~ 0.8 by more than an order of magnitude. We investigate the evolution in the
MZ and LZ relations in comparison with local MZ and LZ relations determined in
a consistent manner using ~21,000 galaxies in the Sloan Digital Sky Survey. We
show that high stellar mass galaxies (log(M/M_solar)~10.6) at z ~ 0.8 have
attained the chemical enrichment seen in the local universe, while lower
stellar mass galaxies (log(M/M_solar)~9.2) at z ~ 0.8 have lower metallicities
(Delta log(O/H)~0.15 dex) than galaxies at the same stellar mass in the local
universe. We find that the LZ relation evolves in both metallicity and B-band
luminosity between z ~ 0.8 and z~ 0, with the B-band luminosity evolving as a
function of stellar mass. We emphasize that the B-band luminosity should not be
used as a proxy for stellar mass in chemical evolution studies of star-forming
galaxies. Our study shows that both the metallicity evolution and the B-band
luminosity evolution for emission-line galaxies between the epochs are a
function of stellar mass, consistent with the cosmic downsizing scenario of
galaxy evolution.Comment: Accepted Version: 18 pages, 13 figure
The Role of Starburst-AGN composites in Luminous Infrared Galaxy Mergers: Insights from the New Optical Classification Scheme
We investigate the fraction of starbursts, starburst-AGN composites,
Seyferts, and LINERs as a function of infrared luminosity (L_IR) and merger
progress for ~500 infrared-selected galaxies. Using the new optical
classifications afforded by the extremely large data set of the Sloan Digital
Sky Survey, we find that the fraction of LINERs in IR-selected samples is rare
(< 5%) compared with other spectral types. The lack of strong infrared emission
in LINERs is consistent with recent optical studies suggesting that LINERs
contain AGN with lower accretion rates than in Seyfert galaxies. Most
previously classified infrared-luminous LINERs are classified as starburst-AGN
composite galaxies in the new scheme. Starburst-AGN composites appear to
"bridge" the spectral evolution from starburst to AGN in ULIRGs. The relative
strength of the AGN versus starburst activity shows a significant increase at
high infrared luminosity. In ULIRGs (L_IR >10^12 L_odot), starburst-AGN
composite galaxies dominate at early--intermediate stages of the merger, and
AGN galaxies dominate during the final merger stages. Our results are
consistent with models for IR-luminous galaxies where mergers of gas-rich
spirals fuel both starburst and AGN, and where the AGN becomes increasingly
dominant during the final merger stages of the most luminous infrared objects.Comment: 30 pages, 19 figures, 10 tables, ApJ accepte
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
Gas-Phase Oxygen Gradients in Strongly Interacting Galaxies: I. Early-Stage Interactions
A consensus is emerging that interacting galaxies show depressed nuclear gas
metallicities compared to isolated star-forming galaxies. Simulations suggest
that this nuclear underabundance is caused by interaction-induced inflow of
metal-poor gas, and that this inflow concurrently flattens the radial
metallicity gradients in strongly interacting galaxies. We present
metallicities of over 300 HII regions in a sample of 16 spirals that are
members of strongly interacting galaxy pairs with mass ratio near unity. The
deprojected radial gradients in these galaxies are about half of those in a
control sample of isolated, late-type spirals. Detailed comparison of the
gradients with simulations show remarkable agreement in gradient distributions,
the relationship between gradients and nuclear underabundances, and the shape
of profile deviations from a straight line. Taken together, this evidence
conclusively demonstrates that strongly interacting galaxies at the present day
undergo nuclear metal dilution due to gas inflow, as well as significant
flattening of their gas-phase metallicity gradients, and that current
simulations can robustly reproduce this behavior at a statistical level.Comment: Accepted for publication in Ap
Examining the role of faith community groups with sexual offenders: A systematic review
The aim of this paper is to examine the role of faith-based communities and activities in helping those convicted of sexual offending to desist from crime and reintegrate back into their communities. It was found that much of the current research is limited to non-offending juvenile populations. Where research has been carried out on adult offenders, these tend to be custodial cases and exclude those convicted of sexual offending. The role of religious and spiritual groups in helping people convicted of sexual offending to desist from crime, while reintegrating into the community is, therefore, unknown. A number of parallels between the factors needed to promote desistance from sexual offending and the conditions encountered when engaged with a faith community are outlined. We would note that a religious and spiritual environment can: promote motivation to change, provide access to pro-social peers, offer moral guidance, provide a support network, and help bring meaning into people's lives. The potential for people to use faith-based communities or organizations to facilitate offending are also considered. Finally, implications for probation work and future research are also discussed
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
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
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