50 research outputs found
Local Analogs for High-redshift Galaxies: Resembling the Physical Conditions of the Interstellar Medium in High-redshift Galaxies
We present a sample of local analogs for high-redshift galaxies selected in
the Sloan Digital Sky Survey (SDSS). The physical conditions of the
interstellar medium (ISM) in these local analogs resemble those in
high-redshift galaxies. These galaxies are selected based on their positions in
the [OIII]/H versus [NII]/H nebular emission-line diagnostic
diagram. We show that these local analogs share similar physical properties
with high-redshift galaxies, including high specific star formation rates
(sSFRs), flat UV continuums and compact galaxy sizes. In particular, the
ionization parameters and electron densities in these analogs are comparable to
those in galaxies, but higher than those in normal SDSS galaxies
by 0.6~dex and 0.9~dex, respectively. The mass-metallicity
relation (MZR) in these local analogs shows ~dex offset from that in SDSS
star-forming galaxies at the low mass end, which is consistent with the MZR of
the galaxies. We compare the local analogs in this study with those
in other studies, including Lyman break analogs (LBA) and green pea (GP)
galaxies. The analogs in this study share a similar star formation surface
density with LBAs, but the ionization parameters and electron densities in our
analogs are higher than those in LBAs by factors of 1.5 and 3, respectively.
The analogs in this study have comparable ionization parameter and electron
density to the GP galaxies, but our method can select galaxies in a wider
redshift range. We find the high sSFR and SFR surface density can increase the
electron density and ionization parameters, but still cannot fully explain the
difference in ISM condition between nearby galaxies and the local
analogs/high-redshift galaxies.Comment: 13 pages, 11 figures, accepted by Ap
How might religion and spirituality help to reintegrate those convicted of sexual offending and how do practitioners respond?
This mixed method study, aims to first, explore the meaning, role, and purpose of religion and spirituality for people convicted of sexual offending. Exploration of their religious and spiritual experiences during periods of offending, incarceration, and desistance from offending, were examined through qualitative in-depth interviews and analysed using Interpretative Phenomenological Analysis. Participants were drawn from prison and community populations. The second phase of the study examined the official risk management process of people convicted of sexual offending. In an effort to understand the extent to which criminal-justice practitioners utilised religious and spiritual communities during the risk-management process; 217 risk management plans were analysed. Results from the first phase of the research suggest that engaging and being affiliated with a religious or spiritual group might: foster the conditions needed to assist the desistance process; provide a context and language for developing non-offending identities; assist with a sense of belonging; help develop hope and manage negative emotions. Unexpectedly, findings from the second phase of the research demonstrated little evidence of practitioners using community groups or religious or spiritual activities as protective factors or supportive mechanisms in the formal risk-management process
Interpreting high [O III]/H β ratios with maturing starbursts
Star-forming galaxies at high redshift show ubiquitously high-ionization parameters, as measured by the ratio of optical emission lines. We demonstrate that local (z < 0.2) sources selected as Lyman break analogues also manifest high line ratios with a typical [O III]/Hβ=3.36+0.14−0.04 – comparable to all but the highest ratios seen in star-forming galaxies at z ∼ 2–4. We argue that the stellar population synthesis code BPASS can explain the high-ionization parameters required through the ageing of rapidly formed star populations, without invoking any AGN contribution. Binary stellar evolution pathways prolong the age interval over which a starburst is likely to show elevated line ratios, relative to those predicted by single stellar evolution codes. As a result, model galaxies at near-solar metallicities and with ages of up to ∼100 Myr after a starburst typically have a line ratio [O III]/Hβ ∼ 3, consistent with those seen in Lyman break galaxies and local sources with similar star formation densities. This emphasises the importance of including binary evolution pathways when simulating the nebular line emission of young or bursty stellar populations
Disentangling AGN and Star Formation in Soft X-rays
We have explored the interplay of star formation and AGN activity in soft
X-rays (0.5-2 keV) in two samples of Seyfert 2 galaxies (Sy2s). Using a
combination of low resolution CCD spectra from Chandra and XMM-Newton, we
modeled the soft emission of 34 Sy2s using power law and thermal models. For
the 11 sources with high signal-to-noise Chandra imaging of the diffuse host
galaxy emission, we estimate the luminosity due to star formation by removing
the AGN, fitting the residual emission. The AGN and star formation
contributions to the soft X-ray luminosity (i.e. L and L)
for the remaining 24 Sy2s were estimated from the power law and thermal
luminosities derived from spectral fitting. These luminosities were scaled
based on a template derived from XSINGS analysis of normal star forming
galaxies. To account for errors in the luminosities derived from spectral
fitting and the spread in the scaling factor, we estimated L and
L from Monte Carlo simulations. These simulated luminosities agree
with L and L derived from Chandra imaging analysis within a
3\sigma\ confidence level. Using the infrared [NeII]12.8\mu m and [OIV]26\mu m
lines as a proxy of star formation and AGN activity, respectively, we
independently disentangle the contributions of these two processes to the total
soft X-ray emission. This decomposition generally agrees with L and
L at the 3\sigma\ level. In the absence of resolvable nuclear
emission, our decomposition method provides a reasonable estimate of emission
due to star formation in galaxies hosting type 2 AGN.Comment: accepted for publication in ApJ; 34 pages, 9 tables, 4 figure
Restoring identity: The use of religion as a mechanism to transition between an identity of sexual offending to a non-offending identity
This study examines the unique experience of participants who during their reintegration back into the community, following a conviction for sexual offending, re-engaged with religious and spiritual communities. To explore meaning Interpretative Phenomenological Analysis (IPA) was adopted. Four in-depth interviews of men convicted for sexual crimes were undertaken and analysed. Findings indicate that through religious affiliation participants were: exposed to new prosocial networks; provided opportunities to seek forgiveness; felt a sense of belonging and affiliation; and were psychologically comforted. However, the study also found that the process of identity transition from ‘offender’ to ‘non-offender’ was not seamless or straightforward for those with an innate sexual deviancy towards children, caution is therefore advised
Optical vs. infrared studies of dusty galaxies and AGN: (I) Nebular emission lines
Optical nebular emission lines are commonly used to estimate the star
formation rate of galaxies and the black hole accretion rate of their central
active nucleus. The accuracy of the conversion from line strengths to physical
properties depends upon the accuracy to which the lines can be corrected for
dust attenuation. For studies of single galaxies with normal amounts of dust,
most dust corrections result in the same derived properties within the errors.
However, for statistical studies of populations of galaxies, or for studies of
galaxies with higher dust contents such as might be found in some classes of
"transition" galaxies, significant uncertainty arises from the dust attenuation
correction. We compare the strength of the predominantly unobscured mid-IR
[NeII]15.5um + [NeIII]12.8um emission lines to the optical H alpha emission
lines in four samples of galaxies: (i) ordinary star forming galaxies, (ii)
optically selected dusty galaxies, (iii) ULIRGs, (iv) Seyfert 2 galaxies. We
show that a single dust attenuation curve applied to all samples can correct H
alpha emission for dust attenuation to a factor better than 2. Similarly, we
compare mid-IR [OIV] and optical [OIII] luminosities to find that [OIII] can be
corrected to a factor better than 3. This shows that the total dust attenuation
suffered by the AGN narrow line region is not significantly different to that
suffered by the starforming HII regions in the galaxy. We provide explicit dust
attenuation corrections, together with errors, for [OII], [OIII] and H alpha.
The best-fit average attenuation curve is slightly greyer than the Milky-Way
extinction law, indicating either that external galaxies have slightly
different typical dust properties to the Milky Way, or that there is a
significant contribution from scattering. Finally, we uncover an intriguing
correlation between Silicate absorption and Balmer decrement.Comment: 19 pages, 9 figures, accepted for publication in MNRA
The ACS Nearby Galaxy Survey Treasury IV. The Star Formation History of NGC 2976
We present resolved stellar photometry of NGC 2976 obtained with the Advanced
Camera for Surveys (ACS) as part of the ACS Nearby Galaxy Survey Treasury
(ANGST) program. The data cover the radial extent of the major axis of the disk
out to 6 kpc, or ~6 scale lengths. The outer disk was imaged to a depth of
M_F606W ~ 1, and an inner field was imaged to the crowding limit at a depth of
M_F606W ~ -1. Through detailed analysis and modeling of these CMDs we have
reconstructed the star formation history of the stellar populations currently
residing in these portions of the galaxy, finding similar ancient populations
at all radii but significantly different young populations at increasing radii.
In particular, outside of the well-measured break in the disk surface
brightness profile, the age of the youngest population increases with distance
from the galaxy center, suggesting that star formation is shutting down from
the outside-in. We use our measured star formation history, along with H I
surface density measurements, to reconstruct the surface density profile of the
disk during previous epochs. Comparisons between the recovered star formation
rates and reconstructed gas densities at previous epochs are consistent with
star formation following the Schmidt law during the past 0.5 Gyrs, but with a
drop in star formation efficiency at low gas densities, as seen in local
galaxies at the present day. The current rate and gas density suggest that
rapid star formation in NGC 2976 is currently in the process of ceasing from
the outside-in due to gas depletion. This process of outer disk gas depletion
and inner disk star formation was likely triggered by an interaction with the
core of the M81 group >~1 Gyr ago that stripped the gas from the galaxy halo
and/or triggered gas inflow from the outer disk toward the galaxy center.Comment: 22 pages, 14 figures, 2 tables, accepted for publication by Ap
Dissecting galaxies: spatial and spectral separation of emission excited by star formation and AGN activity
The optical spectra of Seyfert galaxies are often dominated by emission lines excited by both star formation and active galactic nucleus (AGN) activity. Standard calibrations (such as for the star formation rate) are not applicable to such composite (mixed) spectra. In this paper, we describe how integral field data can be used to spectrally and spatially separate emission associated with star formation from emission associated with accretion on to an AGN. We demonstrate our method using integral field data for two AGN host galaxies (NGC 5728 and NGC 7679) from the Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7). The spectra of NGC 5728 and NGC 7679 form clear sequences of AGN fraction on standard emission line ratio diagnostic diagrams. We show that the emission line luminosities of the majority (>85 per cent) of spectra along each AGN fraction sequence can be reproduced by linear superpositions of the emission line luminosities of one AGN dominated spectrum and one star formation dominated spectrum. We separate the Hα, Hβ, [N II]λ6583, [S II]λλ6716, 6731, [O III]λ5007 and [O II]λλ3726, 3729 luminosities of every spaxel into contributions from star formation and AGN activity. The decomposed emission line images are used to derive the star formation rates and AGN bolometric luminosities for NGC 5728 and NGC 7679. Our calculated values are mostly consistent with independent estimates from data at other wavelengths. The recovered star-forming and AGN components also have distinct spatial distributions which trace structures seen in high-resolution imaging of the galaxies, providing independent confirmation that our decomposition has been successful
Ram pressure feeding super-massive black holes
When supermassive black holes at the center of galaxies accrete matter
(usually gas), they give rise to highly energetic phenomena named Active
Galactic Nuclei (AGN). A number of physical processes have been proposed to
account for the funneling of gas towards the galaxy centers to feed the AGN.
There are also several physical processes that can strip gas from a galaxy, and
one of them is ram pressure stripping in galaxy clusters due to the hot and
dense gas filling the space between galaxies. We report the discovery of a
strong connection between severe ram pressure stripping and the presence of AGN
activity. Searching in galaxy clusters at low redshift, we have selected the
most extreme examples of jellyfish galaxies, which are galaxies with long
tentacles of material extending for dozens of kpc beyond the galaxy disk. Using
the MUSE spectrograph on the ESO Very Large Telescope, we find that 6 out of
the 7 galaxies of this sample host a central AGN, and two of them also have
galactic-scale AGN ionization cones. The high incidence of AGN among the most
striking jellyfishes may be due to ram pressure causing gas to flow towards the
center and triggering the AGN activity, or to an enhancement of the stripping
caused by AGN energy injection, or both. Our analysis of the galaxy position
and velocity relative to the cluster strongly supports the first hypothesis,
and puts forward ram pressure as another, yet unforeseen, possible mechanism
for feeding the central supermassive black hole with gas.Comment: published in Nature, Vol.548, Number 7667, pag.30