60 research outputs found
Reconstructing Merger Timelines Using Star Cluster Age Distributions: The Case of MCG+08-11-002
We present near infrared imaging and integral field spectroscopy of the centre of the dusty luminous infrared galaxy merger MCG+08-11-002, taken using the Near InfraRed Camera 2 (NIRC2) and the OH-Suppressing InfraRed Imaging Spectrograph (OSIRIS) on Keck II. We achieve a spatial resolution of ∼25 pc in the K band, allowing us to resolve 41 star clusters in the NIRC2 images. We calculate the ages of 22/25 star clusters within the OSIRIS field using the equivalent widths of the CO 2.3μm absorption feature and the Brγ nebular emission line. The star cluster age distribution has a clear peak at ages ≲ 20 Myr, indicative of current starburst activity associated with the final coalescence of the progenitor galaxies. There is a possible second peak at ∼65 Myr which may be a product of the previous close passage of the galaxy nuclei. We fit single and double starburst models to the star cluster age distribution and use Monte Carlo sampling combined with two-sided K-S tests to calculate the probability that the observed data are drawn from each of the best fit distributions. There is a >90 per cent chance that the data are drawn from either a single or double starburst star formation history, but stochastic sampling prevents us from distinguishing between the two scenarios. Our analysis of MCG+08-11-002 indicates that star cluster age distributions provide valuable insights into the timelines of galaxy interactions and may therefore play an important role in the future development of precise merger stage classification systems
Probing the physics of narrow-line regions of Seyfert galaxies I: The case of NGC 5427
We have used the Wide Field Spectrograph (WiFeS) on the ANU 2.3m telescope at
Siding Spring to observe the nearby, nearly face-on, Seyfert 2 galaxy, NGC
5427. We have obtained integral field spectroscopy of both the nuclear regions
and the HII regions in the spiral arms. We have constrained the chemical
abundance in the interstellar medium of the extended narrow line region (ENLR)
by measuring the abundance gradient in the circum-nuclear \ion{H}{ii} regions
to determine the nuclear chemical abundances, and to use these to in turn
determine the EUV spectral energy distribution for comparison with theoretical
models. We find a very high nuclear abundance, times solar, with
clear evidence of a nuclear enhancement of N and He, possibly caused by massive
star formation in the extended (pc) central disk structure. The
circum-nuclear narrow-line region spectrum is fit by a radiation pressure
dominated photoionisation model model with an input EUV spectrum from a Black
Hole with mass radiating at of its Eddington
luminosity. The bolometric luminosity is closely constrained to be erg s. The EUV spectrum characterised by
a soft accretion disk and a harder component extending to above 15keV. The ENLR
region is extended in the NW-SE direction. The line ratio variation in
circum-nuclear spaxels can be understood as the result of mixing \ion{H}{ii}
regions with an ENLR having a radius-invariant spectrum.Comment: Accepted for publication in Astronomy and Astrophysics, 14 pages, 13
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ZFIRE: A KECK/MOSFIRE Spectroscopic Survey of Galaxies in Rich Environments at z~2
We present an overview and the first data release of ZFIRE, a spectroscopic
redshift survey of star-forming galaxies that utilizes the MOSFIRE instrument
on Keck-I to study galaxy properties in rich environments at . ZFIRE
measures accurate spectroscopic redshifts and basic galaxy properties derived
from multiple emission lines. The galaxies are selected from a stellar mass
limited sample based on deep near infra-red imaging () and
precise photometric redshifts from the ZFOURGE and UKIDSS surveys as well as
grism redshifts from 3DHST. Between 2013--2015 ZFIRE has observed the COSMOS
and UDS legacy fields over 13 nights and has obtained 211 galaxy redshifts over
from a combination of nebular emission lines (such as \Halpha,
\NII, \Hbeta, \OII, \OIII, \SII) observed at 1--2\micron. Based on our
medium-band NIR photometry, we are able to spectrophotometrically flux
calibrate our spectra to \around10\% accuracy. ZFIRE reaches emission
line flux limits of \around with a
resolving power of and reaches masses down to \around10\msol. We
confirm that the primary input survey, ZFOURGE, has produced photometric
redshifts for star-forming galaxies (including highly attenuated ones) accurate
to with outliers. We measure a
slight redshift bias of , and we note that the redshift bias tends to
be larger at higher masses. We also examine the role of redshift on the
derivation of rest-frame colours and stellar population parameters from SED
fitting techniques. The ZFIRE survey extends spectroscopically-confirmed samples across a richer range of environments, here we make available the
first public release of the data for use by the
community.\footnote{\url{http://zfire.swinburne.edu.au}}Comment: Published in ApJ. Data available at http://zfire.swinburne.edu.au,
Code for figures at https://github.com/themiyan/zfire_survey, 31 pages, 24
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Probing the Physics of Narrow Line Regions in Active Galaxies II: The Siding Spring Southern Seyfert Spectroscopic Snapshot Survey (S7)
Here we describe the \emph{Siding Spring Southern Seyfert Spectroscopic
Snapshot Survey} (S7) and present results on 64 galaxies drawn from the first
data release. The S7 uses the Wide Field Spectrograph (WiFeS) mounted on the
ANU 2.3m telescope located at the Siding Spring Observatory to deliver an
integral field of ~ arcsec at a spectral resolution of in
the red (nm), and in the blue (nm). {From these data
cubes we have extracted the Narrow Line Region (NLR) spectra from a 4 arc sec
aperture centred on the nucleus. We also determine the H and
[OIII]~5007 fluxes in the narrow lines, the nuclear reddening, the
reddening-corrected relative intensities of the observed emission lines, and
the H and \lOIII\ luminosities {determined from spectra for which the
stellar continuum has been removed.} We present a set of images of the galaxies
in [OIII]~5007, [NII]~6584 and H which serve to
delineate the spatial extent of the extended narrow line region (ENLR) and {\bf
also to} reveal the structure and morphology of the surrounding \HII\ regions.
Finally, we provide a preliminary discussion of those Seyfert~1 and Seyfert~2
galaxies which display coronal emission lines in order to explore the origin of
these lines.Comment: Accepted for publication 9 Jan 2015, Astrophysical Journal
Supplements. 49pages, 8 figure
S7 : Probing the physics of Seyfert Galaxies through their ENLR & HII Regions
Here we present the first results from the Siding Spring Southern Seyfert
Spectroscopic Snapshot Survey (S7) which aims to investigate the physics of
~140 radio-detected southern active Galaxies with z<0.02 through Integral Field
Spectroscopy using the Wide Field Spectrograph (WiFeS). This instrument
provides data cubes of the central 38 x 25 arc sec. of the target galaxies in
the waveband 340-710nm with the unusually high resolution of R=7000 in the red
(530-710nm), and R=3000 in the blue (340-560nm). These data provide the
morphology, kinematics and the excitation structure of the extended narrow-line
region, probe relationships with the black hole characteristics and the host
galaxy, measures host galaxy abundance gradients and the determination of
nuclear abundances from the HII regions. From photoionisation modelling, we may
determine the shape of the ionising spectrum of the AGN, discover whether AGN
metallicities differ from nuclear abundances determined from HII regions, and
probe grain destruction in the vicinity of the AGN. Here we present some
preliminary results and modelling of both Seyfert galaxies observed as part of
the survey.Comment: 6 pages, 2 figures, Invited Talk at the IAU symposium 30
Probing the Physics of Narrow Line Regions in Active Galaxies III: Accretion and Cocoon Shocks in the LINER NGC1052
We present Wide Field Spectrograph (WiFeS) integral field spectroscopy and
HST FOS spectroscopy for the LINER galaxy NGC 1052. We infer the presence of a
turbulent accretion flow forming a small-scale accretion disk. We find a
large-scale outflow and ionisation cone along the minor axis of the galaxy.
Part of this outflow region is photoionised by the AGN, and shares properties
with the ENLR of Seyfert galaxies, but the inner (~arcsec)
accretion disk and the region around the radio jet appear shock excited. The
emission line properties can be modelled by a "double shock" model in which the
accretion flow first passes through an accretion shock in the presence of a
hard X-ray radiation, and the accretion disk is then processed through a cocoon
shock driven by the overpressure of the radio jets. This model explains the
observation of two distinct densities ( and cm),
and provides a good fit to the observed emission line spectrum. We derive
estimates for the velocities of the two shock components and their mixing
fractions, the black hole mass, the accretion rate needed to sustain the LINER
emission and derive an estimate for the jet power. Our emission line model is
remarkably robust against variation of input parameters, and so offers a
generic explanation for the excitation of LINER galaxies, including those of
spiral type such as NGC 3031 (M81).Comment: Accepted for publication in Astrophysical Journal. 16 pages, 12
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Dissecting Galaxies: Separating Star Formation, Shock Excitation and AGN Activity in the Central Region of NGC 613
The most rapidly evolving regions of galaxies often display complex optical
spectra with emission lines excited by massive stars, shocks and accretion onto
supermassive black holes. Standard calibrations (such as for the star formation
rate) cannot be applied to such mixed spectra. In this paper we isolate the
contributions of star formation, shock excitation and active galactic nucleus
(AGN) activity to the emission line luminosities of individual spatially
resolved regions across the central 3 3 kpc region of the active
barred spiral galaxy NGC613. The star formation rate and AGN luminosity
calculated from the decomposed emission line maps are in close agreement with
independent estimates from data at other wavelengths. The star formation
component traces the B-band stellar continuum emission, and the AGN component
forms an ionization cone which is aligned with the nuclear radio jet. The
optical line emission associated with shock excitation is cospatial with strong
and [Fe II] emission and with regions of high ionized gas velocity
dispersion ( km s). The shock component also traces the
outer boundary of the AGN ionization cone and may therefore be produced by
outflowing material interacting with the surrounding interstellar medium. Our
decomposition method makes it possible to determine the properties of star
formation, shock excitation and AGN activity from optical spectra, without
contamination from other ionization mechanisms.Comment: 16 pages, 12 figures. Accepted for publication in MNRA
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