Abstract:

A sample of edge-on spiral galaxies aimed at a thorough study of the main structural and photometric parameters of edge-on galaxies, both of early- and late-types, is presented. The data were taken from the Two Micron All Sky Survey (2MASS) in the J, H and K_s filters. The sources were selected according to their angular size mainly on the basis of the 2MASS-selected Flat Galaxy Catalog (2MFGC). The sample consists of 175 galaxies in the K_s filter, 169 galaxies in the H filter and 165 galaxies in the J filter. We present bulge and disc decompositions of each galaxy image. All galaxies have been modelled with a Sérsic bulge and exponential disc with the BUDDA v2.1 package. Bulge and disc sizes, profile shapes, surface brightnesses are provided. Our sample is the biggest up-to-date sample of edge-on galaxies with derived structural parameters for discs and bulges. In this paper, we present the general results of the study of this sample. We determine several scaling relations for bulges and discs which indicate a tight link between their formation and evolution. We show that galaxies with bulges fitted by the Sérsic index n≲ 2 have quite different distributions of their structural parameters than galaxies with n≳ 2 bulges. At a first approximation the Sérsic index threshold n≃ 2 can be used to identify pseudobulges and classical bulges. Thus, the difference in parameter distributions and scaling relations for these subsamples suggests that two or more processes are responsible for disc galaxy formation. The main conclusions of our general statistical analysis of the sample are as follows.

• The distribution of the apparent bulge axis ratio q_b for the subsample with n≲ 2 can be attributed to triaxial, nearly prolate bulges that are seen from different projections, while n≳ 2 bulges seem to be oblate spheroids with moderate flattening. Triaxiality of late-type bulges may be due to the presence of a bar that thickened in the vertical direction during its secular evolution.
• For the sample galaxies, the effective radius of the bulge r_e,b, the disc scalelength h and the disc scaleheight z₀ are well correlated. However, there is a clear trend for the ratio r_e,b/h to increase with n. As n is an indicator of the Hubble type, such a trend unambiguously rules out the widely discussed hypothesis of a scale-free Hubble sequence. The found correlation between z₀ and r_e,b is new and was not described earlier.
• There is a hint that the fundamental planes of discs, which links only disc parameters and the maximum rotational velocity of gas, are different for galaxies with different bulges. This may indicate a real difference of discs in galaxies with low- and high-concentration bulges.
• The most surprising result arises from the investigation of the photometric plane of sample bulges. It turns that the plane is not flat and has a prominent curvature towards small values of n. For bulges, this fact was not noted earlier.
• The clear relation between the flattening of stellar discs h/z₀ and the relative mass of a spherical component, including a dark halo, is confirmed not for bulgeless galaxies but for galaxies with massive bulges.

Many of our results are in good agreement with the results of other authors, several ones are new. Thus, our sample is very useful for further detailed studying and modelling of the edge-on spiral galaxies.

Abstract: Mechanisms proposed to account for observed relationships between the occurrence of solar flares and cosmic-ray decreases at the earth are examined by using a large fraction of all existing standardized flare data obtained from a continuously monitored sun. The interval studied extends from July 1957 through July 1968. A total of 76 cosmic-ray decreases were identified during this interval. By using epoch analysis as well as inspection of the original data, it was found that active flare-producing regions crossed central meridian just before the cosmic-ray decreases began. It was also found that a broad maximum in class 2 or greater flares occurred just before the decreases occurred. However, the flares forming this maximum were observed on the eastern part of the solar disk. Epoch analysis of decreases with greater amplitude show the same relationships to the occurrence of flares. Even the most intense decreases that were thought to be the result of specific known flares show a direct relationship to the time of central-meridian passage of active flare-producing regions. We conclude that our hypothesis that all large transient cosmic-ray decreases can be accounted for by interplanetary structure associated with active flare-producing regions is consistent with the data. Further, we find that, if such flare-producing regions are the site of class 2 or greater flares as they approach central meridian, the likelihood of a decrease at the earth is slightly increased.

Abstract: The authors assumed the existence of a long-lived stream structure in the interplanetary magnetic field during late March 1966. The main feature of this stream was a uniform, high-field core that passed the earth on March 24. The geomagnetic activity, anisotropy of solar particles over the energy range 0.6 to ∼100 Mev/nucleon, and the anisotropy of the Forbush decrease, which were observed during the event, were analyzed and were all found to be compatible with the proposed stream structure.

Abstract: The authors hypothesize that individual flares are not the cause of either Forbush decreases or geomagnetic storms. Evidence supporting this hypothesis is here presented showing that geomagnetic storms and Forbush decreases can be accounted for entirely by the effects of interplanetary ‘streams.’ Major cosmic-ray variations begin near the time that a flare-producing region on the sun passes central meridian. This relationship and a similar relationship between geomagnetic storms and flare-producing regions is shown to exist even during the intervals that include the energetic flares that have produced ground-level increases in neutron monitor counts. Streams, closely associated with these flare-producing regions, are usefully described by the structure in the interplanetary magnetic field since fluctuations in the interplanetary field are highly correlated with the Kp index and the interplanetary field strength is inversely correlated with the cosmic-ray intensity. Such stream structure is used to account for the observed ‘center limb effect.’ It is also shown that when flares of importance 3— or greater occur within a few days of very high geomagnetic activity and at longitudes greater than 25° west, the major geomagnetic activity precedes the flare. This result is not easily explained by the hypothesis that periods of intense geomagnetic activity are due to individual flare effects.