52 research outputs found
Discovery of a deep Seyfert-2 galaxy at z = 0.222 behind NGC 300
We report on the unveiling of the nature of the unidentified X-ray source
3XMM J005450.3-373849 as a Seyfert-2 galaxy located behind the spiral galaxy
NGC 300 using Hubble Space Telescope data, new spectroscopic Gemini
observations and available XMM-Newton and Chandra data. We show that the X-ray
source is positionally coincident with an extended optical source, composed by
a marginally resolved nucleus/bulge, surrounded by an elliptical disc-like
feature and two symmetrical outer rings. The optical spectrum is typical of a
Seyfert-2 galaxy redshifted to z=0.222 +/- 0.001, which confirms that the
source is not physically related to NGC 300. At this redshift the source would
be located at 909+/-4 Mpc (comoving distance in the standard model). The X-ray
spectra of the source are well-fitted by an absorbed power-law model. By tying
between the six available spectra, we found a variable index
running from ~2 in 2000-2001 years, to 1.4-1.6 in the 2005-2014
period. Alternatively, by tying , we found variable absorption columns
of N_H ~ 0.34 x cm in 2000-2001 years, and 0.54-0.75 x
cm in the 2005-2014 period. Although we cannot distinguish
between an spectral or absorption origin, from the derived unabsorbed X-ray
fluxes, we are able to assure the presence of long-term X-ray variability.
Furthermore, the unabsorbed X-ray luminosities of 0.8-2 x 10 erg
s derived in the X-ray band are in agreement with a weakly obscured
Seyfert-2 AGN at .Comment: MNRAS, accepte
Optical polarimetric observations of the microquasar LS 5039
We present the first optical polarimetric observations of the runaway microquasar LS 5039. Our results reveal the presence of a large amount (∼5%) of polarized emission towards this binary system. By combining polarimetric and spectroscopic observations of some stars in the field together with available statistical information on the galactic interstellar polarization of the region, we have estimated and subtracted the contribution of the interstellar polarization in this direction. As a result, we obtain an intrinsic polarization of ∼3% for the object, much higher than what would be expected from jet emission in the optical domain. We suggest that the polarized light originates by electron Thomson scattering in the stellar envelope of the companion star. This allows us to constrain the size of the region where the polarized emission originates, as well as estimating the scattering electronic density and the wind velocity at such distance.Facultad de Ciencias Astronómicas y GeofÃsica
The low-luminosity galaxy population in the NGC 5044 Group (Conference proceeding)
Detailed surface photometry for 79 (mostly dwarf) galaxies in the NGC 5044
Group area is analysed, revealing the existence of different morphologies among
objects originally classified as early-type dwarfs. Particularly, a significant
fraction of bright dwarf "ellipticals" show a distinct bulge+disc structure; we
thus re-classify these objects as dwarf lenticulars (dS0). Our finding points
at a possible scenario where these systems are the remnants of "harassed" disc
galaxies. This is emphasized by the discovery of a few objects with hints for
very low-surface brightness spiral-like structure. The colours, structure, and
spatial distribution of the different galaxy types suggest that our
classification may indeed be separating objects with different origins and/or
evolutionary paths.Comment: 5 pages. To appear in ESO Astrophysics Symposia: "Groups of Galaxies
in the Nearby Universe
PKS 1622-253: A weakly accreting, powerful gamma-ray source
We discuss new deep radio observations of PKS 1622-253 and their implications for the energetics of the central engine that powers this strong high-energy gamma-ray source. Combining archival infrared and optical measurements with new millimeter observations, we show that even though the accretion flow in PKS 1622-253 is underluminous by quasar standards, a powerful superluminal jet is launched with a higher kinetic luminosity than most EGRET blazars. Only a few percent of the total jet kinetic luminosity is required to power even the most powerful gamma-ray flares that are observed. The implication is that a high-accretion system is not required in order to power the strongest high-energy gamma-ray sources.Facultad de Ciencias Astronómicas y GeofÃsica
The Ionized Gas Kinematics of the LMC-Type Galaxy NGC 1427A in the Fornax Cluster
NGC 1427A is a LMC-like irregular galaxy in the Fornax cluster with an
extended pattern of strong star formation around one of its edges, which is
probably due to some kind of interaction with the cluster environment. We
present H-alpha velocities within NGC 1427A, obtained through long-slit
spectroscopy at seven different positions, chosen to fall on the brightest HII
regions of the galaxy. Due to its location very near the center of the cluster
this object is an excellent candidate to study the effects that the cluster
environment has on gas-rich galaxies embedded in it. The rotation of NGC 1427A
is modeled in two different ways. The global ionized gas kinematics is
reasonably well described by solid-body rotation, although on small scales it
shows a chaotic behaviour. In this simple model, the collision with a smaller
member of the cluster as being responsible for the peculiar morphology of NGC
1427A is very unlikely, since the only candidate intruder falls smoothly into
the general velocity pattern of the main galaxy. In a more elaborate model, for
which we obtain a better solution, this object does not lie in the same plane
of NGC 1427A, in which case we identify it as a satellite bound to the galaxy.
These results are discussed in the context of a normal irregular versus one
interacting with some external agent. Based on several arguments and
quantitative estimates, we argue that the passage through the hot intracluster
gas of the Fornax cluster is a very likely scenario to explain the
morphological properties of NGC 1427A.Comment: 31 pages, LaTeX2e, uses aas2pp4.sty and psfig.sty, including 7
Postscript figures; accepted for publication in ApJ, Vol. 530, February 200
Optical Monitoring of 3C 390.3 from 1995 to 2004 and Possible Periodicities in the Historical Light Curve
We report V, R, and I band CCD photometry of the radio galaxy 3C 390.3
obtained with the 1.56-m telescope of the Shanghai Astronomical Observatory
from March 1995 to August 2004. Combining these data with data from the
literature, we have constructed a historical light curve from 1894 to 2004 and
searched for periodicities using the CLEANest program. We find possible periods
of 8.30+-1.17, 5.37+-0.49, 3.51+-0.21, and 2.13+-0.08 years.Comment: Accepted by AJ, 34 pages, 11 figure
PKS 1622-253: A Weakly Accreting, Powerful Gamma Ray Source
In this Letter, we discuss new deep radio observations of PKS 1622-253 and
their implications for the energetics of the central engine that powers this
strong high energy gamma-ray source. Combining archival infrared and optical
measurements with new millimeter observations, we show that even though the
accretion flow in PKS 1622-253 is under-luminous by quasar standards, a
powerful super-luminal jet is launched with a higher kinetic luminosity than
most EGRET blazars. Only a few percent of the total jet kinetic luminosity is
required to power even the most powerful gamma ray flares that are observed.
The implication is that a high accretion system is not required to power the
strongest high energy gamma ray sources.Comment: To appear in ApJ Letter
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