Faint Shell Research Articles

Nature of the diffuse emission sources in the H i supershell in the galaxy IC 1613

ABSTRACT We present a study of the nearby low-metallicity dwarf galaxy IC 1613, focusing on the search for massive stars and related feedback processes, as well as for faint supernova remnants (SNR) in late stages of evolution. We obtained the deepest images of IC 1613 in the narrow-band H α, He ii and [S ii] emission lines and new long-slit spectroscopy observations using several facilities (6-m BTA, 2.5m SAI MSU, and 150RTT telescopes), in combination with the multiwavelength archival data from MUSE/VLT, VLA, XMM–Newton, and Swift/XRT. Our deep narrow-band photometry identifies several faint shells in the galaxy, and we further investigate their physical characteristics with the new long-slit spectroscopy observations and the archival multiwavelength data. Based on energy balance calculations and assumptions about their possible nature, we propose that one of the shells is a possible remnant of a supernova explosion. We study five out of eight Wolf–Rayet (WR) star candidates previously published for this galaxy using the He ii emission line mapping, MUSE/VLT archival spectra, and new long-slit spectra. Our analysis discards the considered WR candidates and finds no new ones. We found P Cyg profiles in H α line in two stars, which we classify as Luminous Blue Variable (LBV) star candidates. Overall, the galaxy IC 1613 may have a lower rate of WR star formation than previously suggested.

SDSS-IV MaNGA – gas rotation velocity lags in the final sample of MaNGA galaxies

ABSTRACT We consider the largest sample of 561 edge-on galaxies observed with integral field units by the MaNGA survey and find 300 galaxies where the ionized gas shows a negative vertical gradient (lag) in its rotational speed. We introduce the stop altitude as the distance to the galactic mid-plane at which the gas rotation should stop in the linear approximation. We find correlations between the lags, stop altitude and galactic mass, stellar velocity dispersion, and overall Sersic index. We do not find any correlation of the lags or stop altitude with the star formation activity in the galaxies. We conclude that low-mass galaxies (log(M*/M⊙) < 10) with low-Sersic index and with low-stellar velocity dispersion possess a wider ‘zone of influence’ in the extragalactic gas surrounding them with respect to higher mass galaxies that have a significant spherical component. We estimated the trend of the vertical rotational gradient with radius and find it flat for most of the galaxies in our sample. A small subsample of galaxies with negative radial gradients of lag has an enhanced fraction of objects with aged low-surface brightness structures around them (e.g. faint shells), which indicates that noticeable accretion events in the past affected the extraplanar gas kinematics and might have contributed to negative radial lag gradients. We conclude that an isotropic accretion of gas from the circumgalactic medium plays a significant role in the formation of rotation velocity lags.

On the Expansion, Age, and Origin of the Puzzling Shell/Pulsar-wind Nebula G310.6–1.6

Abstract We present a 142 ks Chandra observation of the enigmatic combination supernova remnant G310.6–1.6 consisting of a bright pulsar-wind nebula driven by an energetic pulsar, surrounded by a highly circular, very faint shell with a featureless, probably synchrotron, spectrum. Comparison with an observation 6 yr earlier shows no measurable expansion of the shell, though some features in the pulsar-wind nebula have moved. We find an expansion age of at least 2500 yr, implying a current shock velocity less than about 1000 km s−1. We place severe upper limits on thermal emission from the shell; if the shell locates the blast wave, a Sedov interpretation would require the remnant to be very young, about 1000 yr, and to have resulted from a dramatically sub-energetic supernova, ejecting ≪0.02M ⊙ with energy E ≲ 3 × 1047 erg. Even a merger-induced collapse of a white dwarf to a neutron star, with a low-energy explosion, is unlikely to produce such an event. Other explanations seem equally unlikely.

Discovery of an old nova shell surrounding the cataclysmic variable V1315 Aql

Following our tentative discovery of a faint shell around V1315 Aql reported in Sahman et al. (2015), we undertook deep Halpha imaging and intermediate-resolution spectroscopy of the shell. We find that the shell has its geometric centre located on V1315 Aql. The mass, spectral features and density of the shell are consistent with other nova shells, rather than planetary nebulae or supernova remnants. The radial velocity of the shell is consistent with the systemic velocity of V1315 Aql. We believe this evidence strongly suggests that the shell originates from an earlier nova event. This is the first nova shell discovered around a novalike, and supports the theory of nova-induced cycles in mass transfer rates (hibernation theory) first proposed by Shara et al. (1986).

Searching for nova shells around cataclysmic variables

We present the results of a search for nova shells around 101 cataclysmic variables (CVs), using Halpha images taken with the 4.2-m William Herschel Telescope (WHT) and the 2.5-m Isaac Newton Telescope Photometric Halpha Survey of the Northern Galactic Plane (IPHAS). Both telescopes are located on La Palma. We concentrated our WHT search on nova-like variables, whilst our IPHAS search covered all CVs in the IPHAS footprint. We found one shell out of the 24 nova-like variables we examined. The newly discovered shell is around V1315 Aql and has a radius of approx.2.5 arcmin, indicative of a nova eruption approximately 120 years ago. This result is consistent with the idea that the high mass-transfer rate exhibited by nova-like variables is due to enhanced irradiation of the secondary by the hot white dwarf following a recent nova eruption. The implications of our observations for the lifetime of the nova-like variable phase are discussed. We also examined 4 asynchronous polars, but found no new shells around any of them, so we are unable to confirm that a recent nova eruption is the cause of the asynchronicity in the white dwarf spin. We find tentative evidence of a faint shell around the dwarf nova V1363 Cyg. In addition, we find evidence for a light echo around the nova V2275 Cyg, which erupted in 2001, indicative of an earlier nova eruption approx.300 years ago, making V2275 Cyg a possible recurrent nova.

Expansion velocities of the planetary nebula NGC 7009—the high dispersion spectra line profiles

We investigated the line profiles of the high dispersion spectra of He I, He II, N III, [N II], [O III], [Ar III], [Ar IV], [S II], [S III ], and [Cl IV], secured at the center of the planetary nebula NGC 7009 with the fiber-fed Bohyunsan Echelle Spectrograph (BOES). The expansion velocities for the main shell and the faint outer thin shell were derived based on stronger double Gaussian profiles and the fast blue wing component, respectively. With the Keck 2D spectral images, we set the main shell boundaries as R∼4″ and 6″ and the faint outer thin shell boundaries as R∼11″ and 13″. The radial variation of expansion velocities of both shells does not follow a linear acceleration. The acceleration of the main shell gas seems to be in a retarded mode, while that of the outer faint shell gas seems to be affected by an additional force. The fast wing component appears also in the He I, He II, and N III line profiles which are likely to have been formed in a compact region, located inside the main shell. The additional deceleration factor, such as the rotation of the central star or the dust gas in the gas shell might cause the non-linear acceleration. Based on the line profiles responsible for the three zones, we conclude that there were at least three major changes occurred in the central star temperature since the first outflow from the central star.

New perspectives on the supernova remnant G78.2+2.1

Aims. The Galactic object G78.2+2.1 is a classical shell-type supernova remnant. Previous radio continuum studies have shown substantial variations in spectral index across the object. Existing studies of the neutral hydrogen are of relatively low resolution and sensitivity. Much higher sensitivity and resolution data from the Canadian Galactic Plane Survey justify a re-examination of the properties of this SNR. Methods. In order to improve the accuracy of spectral index determination and its spatial variation, we first remove the underlying thermal emission with the use of a correlation between the 60 μm infrared continuum and 1420 MHz radio continuum. We use the so-called TT-plot technique to obtain the continuum spectral index between 408 and 1420 MHz. We also apply a technique to investigate the spectral index variations, while keeping the full resolution of the data. Complementary X-ray and infrared data are used to study associated structures in both continuum and in the 21 cm line of neutral hydrogen. Results. The spectral index a (S v ∞ v -α ) averaged over the SNR is 0.75 ± 0.03, significantly higher than previous studies. The TT-plots and tomography image show spatial variations ranging from as low as 0.40 to as high as 0.80. Two complementary neutral hydrogen structures at LSR velocities of 5.5 and -14 km s -1 , respectively, are shown to circumscribe the continuum emission. A number of scenarios are presented to account for the observed properties. A faint shell to the north-west of the SNR is visible in both radio and infrared continuum as well as in neutral hydrogen, and could be associated with a local blowout of the SNR blast wave into a medium of lower density. An isolated cloudlet probably accelerated by the SNR blast wave shows considerable structure in neutral hydrogen emission, suggesting the cloudlet is either beginning to dissolve within the SNR or is interacting with neighbouring gas. The previously proposed cloudlet at ∼-117 km s -1 is not isolated, but is part of a more extended structure, and is thus unlikely an accelerated cloudlet.

Dense, Fe‐rich Ejecta in Supernova Remnants DEM L238 and DEM L249: A New Class of Type Ia Supernova?

We present observations of two LMC supernova remnants (SNRs), DEM L238 and DEM L249, with the Chandra and XMM-Newton X-ray satellites. Bright central emission, surrounded by a faint shell, is present in both remnants. The central emission has an entirely thermal spectrum dominated by strong Fe L-shell lines, with the deduced Fe abundance in excess of solar and not consistent with the LMC abundance. This Fe overabundance leads to the conclusion that DEM L238 and DEM L249 are remnants of thermonuclear (Type Ia) explosions. The shell emission originates in gas swept up and heated by the blast wave. A standard Sedov analysis implies about 50 solar masses in both swept-up shells, SNR ages between 10,000 and 15,000 yr, low (< 0.05 cm^-3) preshock densities, and subluminous explosions with energies of 3x10^50 ergs. The central Fe-rich supernova ejecta are close to collisional ionization equilibrium. Their presence is unexpected, because standard Type Ia SNR models predict faint ejecta emission with short ionization ages. Both SNRs belong to a previously unrecognized class of Type Ia SNRs characterized by bright interior emission. Denser than expected ejecta and/or a dense circumstellar medium around the progenitors are required to explain the presence of Fe-rich ejecta in these SNRs. Substantial amounts of circumstellar gas are more likely to be present in explosions of more massive Type Ia progenitors. DEM L238, DEM L249, and similar SNRs could be remnants of ``prompt'' Type Ia explosions with young (~100 Myr old) progenitors.

Changes in Ellipticals Due to Collisions with Spirals and Their Consequences

A study of collisions between spiral and elliptical galaxies (approximated as composite spherical masses) is made to assess the changes undergone by the elliptical. Results indicate that unless the spiral is extremely massive compared to the elliptical, the elliptical is almost unaffected, while the spiral is strongly affected. For the frequent type of collision between equally massive spiral and elliptical galaxies, the elliptical is negligibly affected, while disruptive effects set in the spiral. However, the stellar pattern of the elliptical is changed and the stars are found to crowd in faint shells after the collision. The consequences of these results are explored in the context of the morphology-density relationship and the elliptical companions of ring galaxies.

Chandra Studies of Supernova Remnants and Pulsars

With sub-arcsecond angular resolution accompanied by fast time resolution and spatially resolved spectral capabilities, the Chandra X-ray Observatory provides a unique capability for the study of supernova remnants (SNRs) and pulsars. Though in its relative infancy, Chandra has already returned stunning images of SNRs which reveal the distribution of ejecta synthesized in the stellar explosions, the distinct properties of the forward and reverse shocks, and the presence of faint shells surrounding compact remnants. Pulsar observations have uncovered jet features as well as small-scaled structures in synchrotron nebulae. In this brief review we discuss results from early Chandra studies of pulsars and SNRs.

On the Origin of Radial Magnetic Fields in Young Supernova Remnants

We study the radio emission from young supernova remnants by means of three-dimensional numerical MHD simulations of the Rayleigh-Taylor instability in the shell of the remnant. The computation is carried out in spherical polar coordinates (r, θ, ) by using a moving grid technique that allows us to resolve the shell finely. The three-dimensional result shows more turbulent (complex) structures in the mixing region than the two-dimensional result, and the instability is found to deform the reverse shock front. Stokes parameters (I, Q, and U) are computed to study the radio properties of the remnant. The total intensity map shows two distinctive regions (inner and outer shells). The inner shell appears to be complex and turbulent, exhibiting loop structures and plumes as a result of the Rayleigh-Taylor instability, while the outer shell is faint and laminar because of the shocked uniform ambient magnetic fields. The inner shell resembles the observed radio structure in the main shell of young SNRs, which is evidence that the Rayleigh-Taylor instability is an ongoing process in young SNRs. When only the peculiar components of the magnetic fields generated by the instability are considered, the polarization B-vector in the inner radio shell is preferentially radial with about 20%-50% of fractional polarization, which is higher than the observed value. The fractional polarization is lowest in the turbulent inner shell and increases outward, which is attributed to the geometric effect. The polarized intensity is found to be correlated with the total intensity. We demonstrate that the polarized intensity from the turbulent region can dominate over the polarized intensity from the shocked uniform fields if the amplified field is sufficiently strong. Therefore, we conclude that the Rayleigh-Taylor instability can explain the dominant radial magnetic field in the main shell of young supernova remnants. However, the outer faint shell shows a dominant tangential field orientation due to the shock-compression because this region is not mixed by the Rayleigh-Taylor instability, which is contrary to observations. Therefore, another mechanism is necessary to produce the radial components of the magnetic field at the outer shock, which we suggest to be a clumpy medium model.

Hidden supernova remnants in the Large Magellanic Cloud H II complex N44

We have obtained ROSAT PSPC observations of N44, one of the largest H II complexes in the Large Magellanic Cloud. The X-ray emission mostly fails within the ionized shell structures in N44. We find that one faint shell is a classical supernova remnant overlooked by previous surveys. If we model the two largest shells as pressure-driven superbubbles, the predicted X-ray luminosity falls far below the observed value. Instead, we show that off-center supernova remnants hitting superbubble shells can explain the excess X-ray emission.

Discovery of a shell-type supernova remnant in the direction of the young pulsar PSR 1930+22

view Abstract Citations (15) References (26) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Discovery of a Shell-Type Supernova Remnant in the Direction of the Young Pulsar PSR 1930+22 Routledge, D. ; Vaneldik, J. F. Abstract The pulsar PSR 1930+22 has a spin-down age of only 40,000 yr, and has long been considered likely to have an associated radio-detectable supernova remnant (SNR). The authors report 408 and 1420 MHz synthesis observations which reveal a faint shell of nonthermal emission of diameter 1°.7, partly surrounding the position of the pulsar. This may be the expected SNR. The surface brightness-diameter distance of the SNR (4.5 kpc±30%) and the dispersion measure distance of the pulsar (6.6 kpc±30%) agree within the errors. An independent estimate (5.4 kpc±35%) of the SNR distance is provided by the detection of neutral hydrogen which appears to be associated with the SNR shell. Publication: The Astrophysical Journal Pub Date: March 1988 DOI: 10.1086/166133 Bibcode: 1988ApJ...326..751R Keywords: Pulsars; Radio Astronomy; Radio Sources (Astronomy); Supernova Remnants; Astronomical Maps; H Lines; Nonthermal Radiation; Astrophysics; NEBULAE: SUPERNOVA REMNANTS; PULSARS; RADIO SOURCES: IDENTIFICATIONS full text sources ADS | data products SIMBAD (5)

A Shell SNR Associated with PSR1930+22?

AbstractObservations at 408 and 1420 MHz are reported which show a large (1.7 degree diameter) faint shell of nonthermal emission partially surrounding PSR1930+22. This may be the SNR associated with the pulsar, whose spin-down age is only 40000 years.

High-resolution radio observations of the supernova remnant G24.7 + 0.6 and the discovery of an ultracompact H II region

The Crab-like SNR G24.7 + 0.6 with 12 arcmin resolution at 20 cm wavelength has been observed. The image reveals a bright Crab-like core surrounded by a faint shell. An ultracompact H II region lies adjacent to the remnant core and several other compact H II regions lie just outside the remnant shell. Optical, far-infrared, and X-ray observations of the region are also presented. The specific attributes of this remnant and its place in the classification of composite versus Crab-like remnants as well as the general question of the association between Crab-like remnants and H II regions are discussed.

Shells and Encounters of Disk Galaxies with Ellipticals

Faint shells have been found around a large number of ellipticals (Malin and Carter 1980, 1983; Schweizer, 1980). Quinn (1984) has suggested that shells form around ellipticals when a small disk galaxy is tidally disrupted in a near radial orbit. According to this mechanism the remnants of the nearly two-dimensional disk maintain their dimensionality and form sheets. These sheets will phasewrap around the elliptical, and the shells are seen when the line of sight is tangent to one of these surfaces (Quinn 1984, Hernquist and Quinn 1986a,b,c).