455 research outputs found
Photometry and dynamics of the minor mergers AM\,1228-260 and AM\,2058-381
We investigate interaction effects on the dynamics and morphology of the
galaxy pairs AM\,2058-381 and AM\,1228-260. This work is based on images
and long-slit spectra obtained with the Gemini Multi-Object Spectrograph at the
Gemini South Telescope. The luminosity ratio between the main (AM\,2058A) and
secondary (AM\,2058B) components of the first pair is a factor of 5,
while for the other pair, the main (AM\,1228A) component is 20 times more
luminous than the secondary (AM\,1228B). The four galaxies have pseudo-bulges,
with a S\'ersic index . Their observed radial velocities profiles (RVPs)
present several irregularities. The receding side of the RVP of AM\,2058A is
displaced with respect to the velocity field model, while there is a strong
evidence that AM\,2058B is a tumbling body, rotating along its major axis. The
RVPs for AM\,1228A indicate a misalignment between the kinematic and
photometric major axes. The RVP for AM\,1228B is quite perturbed, very likely
due to the interaction with AM\,1228A. NFW halo parameters for AM\,2058A are
similar to those of the Milky Way and M\,31. The halo mass of AM\,1228A is
roughly 10\% that of AM\,2058A. The mass-to-light (M/L) of AM\,2058 agrees with
the mean value derived for late-type spirals, while the low M/L for AM\,1228A
may be due to the intense star formation ongoing in this galaxy.Comment: 20 pages, 10 figures, accepted for publication in MNRA
Interaction effects on galaxy pairs with Gemini/GMOS- II: Oxygen abundance gradients
In this paper we derived oxygen abundance gradients from HII regions located
in eleven galaxies in eight systems of close pairs. Long-slit spectra in the
range 4400-7300A were obtained with the Gemini Multi-Object Spec- trograph at
Gemini South (GMOS). Spatial profiles of oxygen abundance in the gaseous phase
along galaxy disks were obtained using calibrations based on strong
emission-lines (N2 and O3N2). We found oxygen gradients signifi- cantly flatter
for all the studied galaxies than those in typical isolated spiral galaxies.
Four objects in our sample, AM1219A, AM1256B, AM 2030A and AM2030B, show a
clear break in the oxygen abundance at galactocentric radius R/R25 between 0.2
and 0.5. For AM1219A and AM1256B we found negative slopes for the inner
gradients, and for AM2030B we found a positive one. In all these three cases
they show a flatter behaviour to the outskirts of the galaxies. For AM2030A, we
found a positive-slope outer gradient while the inner one is almost compatible
with a flat behaviour. A decrease of star forma- tion efficiency in the zone
that corresponds to the oxygen abundance gradient break for AM1219A and AM2030B
was found. For the former, a minimum in the estimated metallicities was found
very close to the break zone that could be associated with a corotation radius.
On the other hand, AM1256B and AM2030A, present a SFR maximum but not an
extreme oxygen abundance value. All the four interacting systems that show
oxygen gradient breakes the extreme SFR values are located very close to break
zones. Hii regions lo- cated in close pairs of galaxies follow the same
relation between the ionization parameter and the oxygen abundance as those
regions in isolated galaxies.Comment: 30 pages, 14 figures, accepted MNRAS, (Figs. 1 and 2 are in low
resolution
The Highest Resolution Chandra View of Photoionization and Jet-Cloud Interaction in the Nuclear Region of NGC 4151
We report high resolution imaging of the nucleus of the Seyfert 1 galaxy NGC
4151 obtained with a 50 ks Chandra HRC observation. The HRC image resolves the
emission on spatial scales of 0.5", ~30 pc, showing an extended X-ray
morphology overall consistent with the narrow line region (NLR) seen in optical
line emission. Removal of the bright point-like nuclear source and image
deconvolution techniques both reveal X-ray enhancements that closely match the
substructures seen in the Hubble Space Telescope [OIII] image and prominent
knots in the radio jet. We find that most of the NLR clouds in NGC 4151 have
[OIII] to soft X-ray ratio ~10, despite the distance of the clouds from the
nucleus. This ratio is consistent with the values observed in NLRs of some
Seyfert 2 galaxies, which indicates a uniform ionization parameter even at
large radii and a density decreasing as as expected for a nuclear wind
scenario. The [OIII]/X-ray ratios at the location of radio knots show an excess
of X-ray emission, suggesting shock heating in addition to photoionization. We
examine various mechanisms for the X-ray emission and find that, in contrast to
jet-related X-ray emission in more powerful AGN, the observed jet parameters in
NGC 4151 are inconsistent with synchrotron emission, synchrotron self-Compton,
inverse Compton of CMB photons or galaxy optical light. Instead, our results
favor thermal emission from the interaction between radio outflow and NLR gas
clouds as the origin for the X-ray emission associated with the jet. This
supports previous claims that frequent jet-ISM interaction may explain why jets
in Seyfert galaxies appear small, slow, and thermally dominated, distinct from
those kpc scale jets in the radio galaxies.Comment: Accepted for publication in ApJ. 28 pages, 9 figures, 3 table
The Earliest Near-infrared Time-series Spectroscopy of a Type Ia Supernova
We present ten medium-resolution, high signal-to-noise ratio near-infrared
(NIR) spectra of SN 2011fe from SpeX on the NASA Infrared Telescope Facility
(IRTF) and Gemini Near-Infrared Spectrograph (GNIRS) on Gemini North, obtained
as part of the Carnegie Supernova Project. This data set constitutes the
earliest time-series NIR spectroscopy of a Type Ia supernova (SN Ia), with the
first spectrum obtained at 2.58 days past the explosion and covering -14.6 to
+17.3 days relative to B-band maximum. C I {\lambda}1.0693 {\mu}m is detected
in SN 2011fe with increasing strength up to maximum light. The delay in the
onset of the NIR C I line demonstrates its potential to be an effective tracer
of unprocessed material. For the first time in a SN Ia, the early rapid decline
of the Mg II {\lambda}1.0927 {\mu}m velocity was observed, and the subsequent
velocity is remarkably constant. The Mg II velocity during this constant phase
locates the inner edge of carbon burning and probes the conditions under which
the transition from deflagration to detonation occurs. We show that the Mg II
velocity does not correlate with the optical light-curve decline rate
{\Delta}m15. The prominent break at ~1.5 {\mu}m is the main source of concern
for NIR k-correction calculations. We demonstrate here that the feature has a
uniform time evolution among SNe Ia, with the flux ratio across the break
strongly correlated with {\Delta}m15. The predictability of the strength and
the onset of this feature suggests that the associated k-correction
uncertainties can be minimized with improved spectral templates.Comment: 14 pages, 13 figures, accepted for publication in Ap
A Snapshot of the Continuous Emission of the Active Galactic Nucleus in NGC 3783 from Gamma-Ray to Radio Wavelengths
To better understand the physical processes that produce the continuous emission in active galactic nuclei (AGN), a snapshot of the overall continuous energy distribution of NGC 3783, from gamma ray to radio wavelengths, has been obtained within the framework of the World Astronomy Days. The data collected in this campaign are from GRO, ROSAT, Voyager 2, IUE, HST, CTIO, SAAO, and the VLA. Great care has been taken in disentangling the genuine AGN continusous emission from other contributions; depending on the waveband, the latter might be (1) unrelated contaminating sources in cases where the instrument field of view is large (2) components within which the AGN is embedded, such as the stellar bulge population which accounts for a significant fraction of the optical continuum, and free-bound and FE2 blends wich contribute to the ultraviolet flux. After correction for these other contributins, the continuous emission of the isolated AGN appears to be rather flat (i.e., approximately equal energy per unit logarithmic frequency) from soft gamma ray to infrared wavelengths. At high energies (0.1 MeV to 0.1 keV), the AGN continuum can be fitted by a power law F nu approaches Nu(exp -a) with a spectral index of alpha approximately 1. At longer wavelengths, two excesses above this power law ('bumps') appear: in the ultraviolet, the classical big blue bump, which can be interpreted as thermal emission from the accretion disc surrounding a massive black hole, and in the infrared, a second bump which can be ascribed to thermal emission from dust in the vicinity of the AGN, heated by ultraviolet radiation from the central source. By fitting accretion-disk models to the observed AGN spectral energy distribution, we find values for the accretion disk innermost temperature, accretion rate, and black hole mass, with some differences that depend on whether or not we extrapolate the high energy power law up to infrared wavelengths. A fit to the IR bump above the extended alpha equals 1 power law suggests the presence of a dust component covering the region from a distance rho approximately equals 80 light days (hot grains at a temperature of approximately equals 1500 K) to rho approximately equals 60 light years (cool grains at T approximately equals 200 K). The total mass of dust is around 60 solar masses
Interaction effects on galaxy pairs with gemini/GMOS-I: Electron density
We present an observational study about the impacts of the interactions on the electron density of HII regions located in seven systems of interacting galaxies. The data consist of long-slit spectra in the range 4400-7300 Ã…, obtained with the Gemini Multi-Object Spectrograph at Gemini South (GMOS-S). The electron density was determined using the ratio of emission lines [S II] λ6716/λ6731. Our results indicate that the electron density estimates obtained of HII regions from our sample of interacting galaxies are systematically higher than those derived for isolated galaxies. The mean electron density values of interacting galaxies are in the range of Ne = 24-532 cm-3, while those obtained for isolated galaxies are in the range of Ne =40-137 cm-3.Comparing the observed emission lines with predictions of photoionization models, we verified that almost all the HII regions of the galaxies AM 1054A, AM 2058B and AM 2306B have emission lines excited by shock gas. For the remaining galaxies, only few H II regions have emission lines excited by shocks, such as in AM 2322B (one point) and AM 2322A (four points). No correlation is obtained between the presence of shocks and electron densities. Indeed, the highest electron density values found in our sample do not belong to the objects with gas shock excitation. We emphasize the importance of considering these quantities especially when the metallicity is derived for these types of systems.Facultad de Ciencias Astronómicas y GeofÃsicasInstituto de AstrofÃsica de La Plat
Arabidopsis thaliana MIRO1 and MIRO2 GTPases Are Unequally Redundant in Pollen Tube Growth and Fusion of Polar Nuclei during Female Gametogenesis
MIRO GTPases have evolved to regulate mitochondrial trafficking and morphology in eukaryotic organisms. A previous study showed that T-DNA insertion in the Arabidopsis MIRO1 gene is lethal during embryogenesis and affects pollen tube growth and mitochondrial morphology in pollen, whereas T-DNA insertion in MIRO2 does not affect plant development visibly. Phylogenetic analysis of MIRO from plants revealed that MIRO 1 and 2 orthologs in dicots cluster in two separate groups due to a gene/genome duplication event, suggesting that functional redundancy may exists between the two MIRO genes. To investigate this possibility, we generated miro1(+/−)/miro2-2(−/−) plants. Compared to miro1(+/−) plants, the miro1(+/−)/miro2-2(−/−) plants showed increased segregation distortion. miro1(+/−)/miro2-2(−/−) siliques contained less aborted seeds, but more than 3 times the number of undeveloped ovules. In addition, reciprocal crosses showed that co-transmission through the male gametes was nearly absent, whereas co-transmission through the female gametes was severely reduced in miro1(+/−)/miro2-2(−/−) plants. Further investigations revealed that loss of MIRO2 (miro2(−/−)) function in the miro1(+/−) background enhanced pollen tube growth defects. In developing miro1(+/−)/miro2(−/−) embryo sacs, fusion of polar nuclei was further delayed or impaired compared to miro1 plants. This phenotype has not been reported previously for miro1 plants and coincides with studies showing that defects in some mitochondria-targeted genes results in the same phenotype. Our observations show that loss of function in MIRO2 in a miro1(+/−) background enhances the miro1(+/−) phenotype significantly, even though miro2(−/−) plants alone does not display any phenotypes. Based on these findings, we conclude that MIRO1 and MIRO2 are unequally redundant and that a proportion of the miro1(+/−)/miro2(−/−) plants haploid gametes displays the complete null phenotype of MIRO GTPase function at key developmental stages
Multi-wavelength study of the Seyfert 1 galaxy NGC 3783 with XMM-Newton
We present the analysis of multi-wavelength XMM-Newton data from the Seyfert
galaxy NGC 3783, including UV imaging, X-ray and UV lightcurves, the 0.2-10 keV
X-ray continuum, the iron K-alpha emission line, and high-resolution
spectroscopy and modelling of the soft X-ray warm absorber. The 0.2-10 keV
spectral continuum can be well reproduced by a power-law at higher energies; we
detect a prominent Fe K-alpha emission line, with both broad and narrow
components, and a weaker emission line at 6.9 keV which is probably a
combination of Fe K-beta and Fe XXVI. We interpret the significant deficit of
counts in the soft X-ray region as being due to absorption by ionised gas in
the line of sight. This is demonstrated by the large number of narrow
absorption lines in the RGS spectrum from iron, oxygen, nitrogen, carbon, neon,
argon, magnesium, silicon and sulphur. The wide range of iron states present in
the spectrum enables us to deduce the ionisation structure of the absorbing
medium. We find that our spectrum contains evidence of absorption by at least
two phases of gas: a hotter phase containing plasma with a log ionisation
parameter xi (where xi is in erg cm/s) of 2.4 and greater, and a cooler phase
with log xi centred around 0.3. The gas in both phases is outflowing at speeds
of around 800 km/s. The main spectral signature of the cold phase is the
Unresolved Transition Array (UTA) of M-shell iron, which is the deepest yet
observed; its depth requires either that the abundance of iron, in the cold
phase, is several times that of oxygen, with respect to solar abundances, or
that the absorption lines associated with this phase are highly saturated. The
cold phase is associated with ionisation states that would also absorb in the
UV.Comment: 16 pages, 10 figures, accepted by Astronomy & Astrophysics; some
measured wavelengths and blueshifts changed to correct a computing erro
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