8 research outputs found
A reconnaissance of the possible donor stars to the Kepler supernova
The identity of Type Ia supernova progenitors remains a mystery, with various
lines of evidence pointing towards either accretion from a non-degenerate
companion, or the rapid merger of two degenerate stars leading to the
thermonuclear destruction of a white dwarf. In this paper we spectroscopically
scrutinize 24 of the brightest stars residing in the central 38" x 38" of the
SN 1604 (Kepler) supernova remnant to search for a possible surviving companion
star. We can rule out, with high certainty, a red giant companion star - a
progenitor indicated by some models of the supernova remnant. Furthermore, we
find no star that exhibits properties uniquely consistent with those expected
of a donor star down to L>10Lsun. While the distribution of star properties
towards the remnant are consistent with unrelated stars, we identify the most
promising candidates for further astrometric and spectroscopic follow-up. Such
a program would either discover the donor star, or place strong limits on
progenitor systems to luminosities with L<<Lsun.Comment: accepted by Ap
Kinematics and excitation of the molecular hydrogen accretion disc in NGC 1275
We report the results of high spatial and spectral resolution integral-field spectroscopy of the central~3×3 arcsec2 of the active galaxy NGC 1275 (Perseus A), based on observations with the Near-infrared Integral Field Spectrograph (NIFS) and the ALTit
Strong UV and X-ray variability of the Narrow Line Seyfert 1 Galaxy WPVS 007 -- on the nature of the X-ray low state
We report on multi-wavelength observations of the X-ray transient Narrow Line
Seyfert 1 (NLS1) galaxy WPVS 007. The galaxy was monitored with Swift between
October 2005 and July 2013, after it had undergone a dramatic drop in its X-ray
flux earlier. For the first time, we are able to repeatedly detect this NLS1 in
X-rays again. This increased number of detections in the last couple of years
may suggest that the strong absorber that has been found in this AGN is
starting to become leaky, and may eventually disappear. The X-ray spectra
obtained for WPVS 007 are all consistent with a partial covering absorber
model. A spectrum based on the data during the extreme low X-ray flux states
shows that the absorption column density is of the order of 4 x 10^23 cm^-2
with a covering fraction of 95%. WPVS 007 also displays one of the strongest UV
variabilities seen in Narrow Line Seyfert 1s. The UV continuum variability
anti-correlates with the optical/UV slope alpha-UV which suggests that the
variability primarily may be due to reddening. The UV variability time scales
are consistent with moving dust `clouds' located beyond the dust sublimation
radius of approximately 20 ld. We present for the first time near infrared JHK
data of WPVS 007, which reveal a rich emission-line spectrum. Recent optical
spectroscopy does not indicate significant variability in the broad and FeII
emission lines, implying that the ionizing continuum seen by those gas clouds
has not significantly changed over the last decades. All X-ray and UV
observations are consistent with a scenario in which an evolving Broad
Absorption Line (BAL) flow obscures the continuum emission. As such, WPVS 007
is an important target for our understanding of BAL flows in low-mass active
galactic nuclei (AGN).Comment: Accepted for publications in the Astronomical Journal; 29 pages, 10
Figures, 7 Table
Galaxy emission line classification using 3D line ratio diagrams
Two-dimensional (2D) line ratio diagnostic diagrams have become a key tool in
understanding the excitation mechanisms of galaxies. The curves used to
separate the different regions - HII-like or else excited by an active galactic
nucleus (AGN) - have been refined over time but the core technique has not
evolved significantly. However, the classification of galaxies based on their
emission line ratios really is a multi-dimensional problem. Here we exploit
recent software developments to explore the potential of three-dimensional (3D)
line ratio diagnostic diagrams. We introduce a specific set of 3D diagrams, the
ZQE diagrams, which separate the oxygen abundance and the ionisation parameter
of HII region-like spectra, and which also enable us to probe the excitation
mechanism of the gas. By examining these new 3D spaces interactively, we define
a new set of 2D diagnostics, the ZE diagnostics, which can provide the
metallicity of objects excited by hot young stars, and which cleanly separate
HII region-like objects from the different classes of AGNs. We show that these
ZE diagnostics are consistent with the key log[NII]/H vs.
log[OIII]/H diagnostic currently used by the community. They also have
the advantage of attaching a probability that a given object belongs to one
class or to the other. Finally, we discuss briefly why ZQE diagrams can provide
a new way to differentiate and study the different classes of AGNs in
anticipation of a dedicated follow-up study.Comment: 21 pages, 15 figures, accepted for publication in ApJ. Due to size
limitations, the supplementary STL file for the 3D-printable diagram is
available here: http://www.mso.anu.edu.au/~fvogt/online_material.htm
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
figure
The Arp 220 merger on kpc scales
For the first time, we study the eastern nucleus in greater detail and search for the more extended emission in the molecular gas in different CO line transitions of the famous ultraluminous infrared galaxy (ULIRG) Arp 220. Furthermore, we present a model of the merger in Arp 220 on large scales with the help of the CO data and an optical and near-infrared composite Hubble Space Telescope image of the prototypical ULIRG. Using the Plateau de Bure interferometer (PdBI), we obtained CO(2-1) and (1-0) data at wavelengths of 1 and 3mm in 1994, 1996, 1997, and 2006 at different beam sizes and spatial resolutions. The simulations of the merger in Arp 220 were performed with the Identikit modeling tool. The model parameters that describe the galaxy merger best give a mass ratio of 1:2 and result in a merger of 6 × 108yr. The low-resolution CO(1-0) PdBI observations suggest that there are indications for emission 10″ toward the south, as well as to the north and to the west of the two nuclei
Strong uv and x-ray variability of the narrow line Seyfert 1 Galaxy WPVS 007 - On the nature of the x-ray low state
We report on multi-wavelength observations of the X-ray transient Narrow Line Seyfert 1 (NLS1) galaxy WPVS 007. The galaxy was monitored with Swift between 2005 October and 2013 July, after it had previously undergone a dramatic drop in its X-ray flux. F