اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدRadio Continuum Jet in NGC 7479
297
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The barred galaxy NGC 7479 hosts a remarkable jet-like radio continuum feature: bright, 12-kpc long in projection, and hosting an aligned magnetic field. The degree of polarization is 6%-8% along the jet, and remarkably constant, which is consistent with helical field models. The radio brightness of the jet suggests strong interaction with the ISM and hence a location near the disk plane. We observed NGC 7479 at four wavelengths with the VLA and Effelsberg radio telescopes. The equipartition strength is 35-40 micro-G for the total and >10 micro-G for the ordered magnetic field in the jet. The jet acts as a bright, polarized background. Faraday rotation between 3.5 and 6 cm and depolarization between 6 and 22 cm can be explained by magneto-ionic gas in front of the jet, with thermal electron densities of ~0.06 cm**(-3) in the bar and ~0.03 cm**(-3) outside the bar. The regular magnetic field along the bar points toward the nucleus on both sides. The regular field in the disk reveals multiple reversals, probably consisting of field loops stretched by a shearing gas flow in the bar. The projection of the jet bending in the sky plane is in the sense opposite to that of the underlying stellar and gaseous spiral structure. The bending in 3-D is most easily explained as a precessing jet, with an age less than 10**6 years. Our observations are consistent with very recent triggering, possibly by a minor merger. NGC 7479 provides a unique opportunity to study interaction-triggered 15-kpc scale radio jets within a spiral galaxy.
قيم البحث
اقرأ أيضاً
We analyze 3.5 resolution, high sensitivity radio continuum images of the nearby spiral galaxy NGC 4258 at 6 and 20 cm derived from multiple observations used to monitor the radio supernova SN 1981K (Van Dyk et al. 1992, [ApJ, 396, 1995]). Seven brig
ht H II region and five supernova remnant candidates are identified. Extinctions to the H II regions are estimated for the first time from a comparison of radio flux densities to new optical fluxes derived from H-alpha observations by Dutil & Roy (1999, [ApJ, 516, 62]). The bright end of the H II region luminosity function is established at each wavelength. The luminosity functions are best fit by power laws consistent with the shape of previously published radio and optical luminosity functions for a number of galaxies. The supernova remnants are all about 2--3 times the radio luminosity of Cas A. In addition, the galaxys nucleus is shown to have been variable over the SN 1981K monitoring period. The spectral index (alpha) distribution of the anomalous radio arms is investigated and found to be relatively uniform at alpha = -0.65 +/- 0.10.
We study the collimation and acceleration of the jets in the nearby giant radio galaxy NGC 315, using multifrequency Very Long Baseline Array observations and archival High Sensitivity Array and Very Large Array data. We find that the jet geometry tr
ansitions from a semi-parabolic shape into a conical/hyperbolic shape at a distance of $approx10^5$ gravitational radii. We constrain the frequency-dependent position of the core, from which we locate the jet base. The jet collimation profile in the parabolic region is in good agreement with the steady axisymmetric force-free electrodynamic solution for the outermost poloidal magnetic field line anchored to the black hole event horizon on the equatorial plane, similar to the nearby radio galaxies M87 and NGC 6251. The velocity field derived from the asymmetry in brightness between the jet and counterjet shows gradual acceleration up to the bulk Lorentz factor of $Gamma sim 3$ in the region where the jet collimation occurs, confirming the presence of the jet acceleration and collimation zone. These results suggest that the jets are collimated by the pressure of the surrounding medium and accelerated by converting Poynting flux to kinetic energy flux. We discover limb-brightening of the jet in a limited distance range where the angular resolution of our data is sufficient to resolve the jet transverse structure. This indicates that either the jet has a stratified velocity field of fast-inner and slow-outer layers or the particle acceleration process is more efficient in the outer layer due to the interaction with the surroundings on pc-scales.
We report on the 2.5 arcsec (400 pc) resolution CO (J = 1 -> 0) observations covering the whole length of the bar in the strongly barred late-type spiral galaxy NGC 7479. CO emission is detected only along a dust lane that traverses the whole length
of the bar, including the nucleus. The emission is strongest in the nucleus. The distribution of emission is clumpy along the bar outside the nucleus, and consists of gas complexes that are unlikely to be gravitationally bound. The CO kinematics within the bar consist of two separate components. A kinematically distinct circumnuclear disk, < 500 pc in diameter, is undergoing predominantly circular motion with a maximum rotational velocity of 245 km/s at a radius of 1 arcsec (160 pc). The CO-emitting gas in the bar outside the circumnuclear disk has substantial noncircular motions which are consistent with a large radial velocity component, directed inwards. The CO emission has a large velocity gradient across the bar dust lane, ranging from 0.5 to 1.9 km/s/pc after correcting for inclination, and the projected velocity change across the dust lane is as high as 200 km/s. This sharp velocity gradient is consistent with a shock front at the location of the bar dust lane. A comparison of H-alpha and CO kinematics across the dust lane shows that although the H-alpha emission is often observed both upstream and downstream from the dust lane, the CO emission is observed only where the velocity gradient is large. We also compare the observations with hydrodynamic models and discuss star formation along the bar.
We present new continuum VLA observations of the nearby Sy 1.5 galaxy NGC 5033, made at 4.9 and 8.4 GHz on 8 April 2003. Combined with VLA archival observations at 1.4 and 4.9 GHz made on 7 August 1993, 29 August 1999, and 31 October 1999, we sample
the galaxy radio emission at scales ranging from the nuclear regions (<~ 100 pc) to the outer regions of the disk (~ 40 kpc). The high-resolution VLA images show a core-jet structure for the Sy 1.5 nucleus. While the core has a moderately steep non-thermal radio spectrum (S_ u ~ u^alpha; alpha_{1.5}^{4.9} approx -0.4), the inner kpc region shows a steeper spectrum (alpha_{1.5}^{8.4} approx -0.9). This latter spectrum is typical of galaxies where energy losses are high, indicating that the escape rate of cosmic ray electrons in NGC 5033 is low. The nucleus contributes little to the total 1.4 GHz radio power of NGC 5033 and, based on the radio to far-infrared (FIR) relation, it appears that the radio and far-infrared emission from NGC 5033 are dominated by a starburst that during the last 10 Myr produced stars at a rate of ~2.8 M_sun/yr, yielding a supernova (type Ib/c and II) rate of 0.045 #/yr. This supernova rate corresponds to about 1 SN event every 22 yr. Finally, from our deep 8.4 GHz VLA-D image, we suggest the existence of a radio spur in NGC 5033, which could have been due to a hot superbubble formed as a consequence of sequential supernova explosions occurring during the lifetime of a giant molecular cloud.
We present new radio continuum observations, taken at 1.4 GHz with the Very Large Array, and new observations in the CO line, taken with the Plateau de Bure interferometer, of two regions of the spiral galaxy NGC 3627. Comparing these observations wi
th archival Spitzer and H_{alpha} data we study the correlation of the radio continuum (RC), infrared-8 um and CO emissions at a spatial resolution of 100 pc. We compare the point-by-point variations of the RC, CO, and 8um brightnesses in two distinct regions of 2 kpc times 2 kpc in size of NGC 3627. We examined scale much lower than the electron diffusion scale, where a break down of the correlations would be expected. However no evidence for such correlation break down has been found. The RC emission follows well the distribution of CO and the widths of several structures, measured along slices across them, are comparable. Furthermore, we found that down to a spatial scale of 100 pc the radio continuum emission is correlated with dust emissions at 4.5, 5.8, and 8 um, that traces different dust temperatures. We present a new perspective with which visualizing and studying the RC-CO-24 um and RC-CO-8 um correlations, by using a three-dimensional representation. We fit the observed data with a three dimensional line, obtaining a rms of 0.25 dex. The observed correlation enhances the complexity of the electrons diffusion, losses and injection mechanisms, and of their connection to star formation processes, described by molecular and dust emissions. We plan to further investigate this connection using spatially resolved spectral index studies at low radio frequencies where the thermal emission component is seemingly negligible.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
