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1.
Type Ia Supernova (SN Ia) are a powerful, albeit not completely understood, tool for cosmology. Gaps in our understanding of their progenitors and detailed physics can lead to systematic errors in the cosmological distances they measure. We use UV data in two context to help further our understanding of SN Ia progenitors and physics. We analyze a set of nearly 700 light curves, and find no signature of the shock heating of a red giant companion, predicted by Kasen (Astrophys. J. 708:1025, 2010), casting doubt as to frequency of this SN Ia channel. We also use UV imaging of high redshift host galaxies of SN Ia to better understand the environments which SN Ia occur. We show that some high-z elliptical galaxies have current star formation, hindering efforts to use them as low-extinction environments. We show cosmological scatter of SN distances at large effective radii in their hosts is significantly reduced, and argue this is due to the smaller amounts of dust affecting the SN Ia. Finally, we find a two component dependence of SN distance measurements as a function of their host galaxy’s FUV-V color. This indicates that both the age and metallicity/mass of the host galaxy maybe important ingredients in measuring SN Ia distances.  相似文献   

2.
We present narrow band, continuum subtracted Hα, [S ii], Hβ, [O iii] and [O ii] data taken with the Wide Field Camera 3 on the Hubble Space Telescope in the nearby dwarf starburst galaxy NGC 4214. From these images, we identify seventeen new planetary nebula candidates, and seven supernova remnant candidates. We use the observed emission line luminosity function of the planetary nebulae to establish a new velocity-independent distance to NGC 4214. We conclude that the PNLF technique gives a reddening independent distance to NGC 4214 of 3.19±0.36 Mpc, and that our current best-estimate of the distance to this galaxy ids 2.98±0.13 Mpc.  相似文献   

3.
This paper argues that the Milky Way galaxy is probably the largest member of the Local Group. The evidence comes from estimates of the total mass of the Andromeda galaxy (M31) derived from the three-dimensional positions and radial velocities of its satellite galaxies, as well as the projected positions and radial velocities of its distant globular clusters and planetary nebulae. The available data set comprises 10 satellite galaxies, 17 distant globular clusters and nine halo planetary nebulae with radial velocities. We find that the halo of Andromeda has a mass of together with a scalelength of 90 kpc and a predominantly isotropic velocity distribution. For comparison, our earlier estimate for the Milky Way halo is Although the error bars are admittedly large, this suggests that the total mass of M31 is probably less than that of the Milky Way . We verify the robustness of our results to changes in the modelling assumptions and to errors caused by the small size and incompleteness of the data set.
Our surprising claim can be checked in several ways in the near future. The numbers of satellite galaxies, planetary nebulae and globular clusters with radial velocities can be increased by ground-based spectroscopy, while the proper motions of the companion galaxies and the unresolved cores of the globular clusters can be measured using the astrometric satellites Space Interferometry Mission ( SIM ) and Global Astrometric Interferometer for Astrophysics ( GAIA ). Using 100 globular clusters at projected radii 20 R 50 kpc with both radial velocities and proper motions, it will be possible to estimate the mass within 50 kpc to an accuracy of 20 per cent. Measuring the proper motions of the companion galaxies with SIM and GAIA will reduce the uncertainty in the total mass caused by the small size of the data set to 22 per cent.  相似文献   

4.
The planetary nebula populations of relatively nearby galaxies can be easily observed and provide both a distance estimate and a tool with which dynamical information can be obtained. Usually the requisite radial velocities are obtained by multi-object spectroscopy once the planetary nebulae have been located by direct imaging. Here we report on a technique for measuring planetary nebula kinematics using the double-beam ISIS spectrograph at the William Herschel Telescope in a novel slitless mode, which enables the detection and radial velocity measurements to be combined into a single step. The results on our first target, the Sab galaxy NGC 4736, allow the velocity dispersion of the stellar population in a disc galaxy to be traced out to four scalelengths for the first time and are consistent with a simple isothermal sheet model.  相似文献   

5.
We study the bending of jets in binary stellar systems. A compact companion accretes mass from the slow wind of the mass-losing primary star, forms an accretion disc and blows two opposite jets. These fast jets are bent by the slow wind. Disregarding the orbital motion, we find the dependence of the bending angle on the properties of the slow wind and the jets. Bending of jets is observed in planetary nebulae which are thought to be the descendants of interacting binary stars. For example, in some of these planetary nebulae, the two bubbles (lobes) which are inflated by the two opposite jets are displaced to the same side of the symmetry axis of the nebula. Similar displacements are observed in bubble pairs in the centre of some clusters and groups of galaxies. We compare the bending of jets in binary stellar systems with that in clusters of galaxies.  相似文献   

6.
Dependencies of galactic planetary nebula chemical abundances and their central star masses on the distance from the galactic plane are discussed.Z-dependencies of He/H, N/H, N/O and Ar/H and dependencies of He/H, N/H, N/O, Ne/H and Ar/H on central star mass are found. Three galactic planetary nebula distance scale samples are used and it is shown that the distance scale system (where distances of each planetary nebula mass class are determined with the separate scale) is the most reliable. The correlations obtained for the Magellanic Cloud planetary nebulae are used for comparison.  相似文献   

7.
Summary The status of the cosmic distance scale problem in early 1989 is reviewed. Internally consistent distances to Local Group galaxies are given in Tables 5 and 6. Within the Local Group the distance scale is found to be 11±5% smaller than that previously adopted by Sandage and Tammann. Distances to nearby galaxies are used as stepping stones to the Virgo cluster. The interpretation of the Tully-Fisher observations of Virgo spirals is found to be ambiguous because it is not yet clear which spirals are cluster members and which are background objects. Distance estimates of the Virgo cluster obtained by different techniques are listed in Table 11. The distance modulus of the Virgo cluster is found to be 31.5±0.2, corresponding to a distance of 20±2 Mpc. The elliptical galaxies in the core of the Virgo cluster haveV 0=1200±46 kms–1, which corresponds toV LG=1082±48 km s–1. With an infall velocity of 250±50 km s–1 this yields a cosmological redshiftV=1332±69 km s–1, from which a Hubble parameter H0=67±8 km s–1 Mpc–1 is obtained. Space Telescope observations of distant Cepheids, Tully-Fisher observations of spirals in the Hercules eluster, and interference filter observations of Virgo planetary nebulae in the light of [OIII], should soon result in a major improvement in the accuracy with which H0 is known.  相似文献   

8.
Two of the basic building blocks of galaxies are stars and the interstellar medium. The evolution of the abundance composition in the latter and especially the enrichment of heavy elements as a function of space and time reflects in turn the history of star formation and the lifetimes of the diverse contributing stellar objects. Therefore, the understanding of stellar evolution and its endpoints (mainly planetary nebulae, supernovae of type Ia and type II/Ib/Ic) is essential. Despite many efforts, a full and self-consistent understanding of supernovae (the main contributors to nucleosynthesis in galaxies) is not existing, yet. However, they leave fingerprints, seen either in spectra, lightcurves, radioactivities/decay gamma-rays or in galactic evolution. Here we want to address the composition of ejecta, their model uncertainties and relate them to constraints from abundance observations in galactic evolution. This revised version was published online in September 2006 with corrections to the Cover Date.  相似文献   

9.
Summary In the last decade, our understanding of early-type galaxies has greatly changed: from rather uninteresting oblate spheroids flattened by rotation to multicomponent stellar systems whose structure, formation mechanisms, and evolution, are far from being understood. This new scenario is mainly the consequence of the huge growth, in quantity and in quality, of kinematical data obtained from high signal to noise spectral data. Rotation curves and velocity dispersion profiles extending out to almost 2 effective radii are now available, together with line asymmetry measurements, for the stellar components of a fairly large sample of galaxies. For a few galaxies, outer halo tracers such as globular clusters and/or planetary nebulae allow to explore the kinematics out at 4 6r e. In this article we focus on these data giving particular emphasis on the most recent results. Reference is given to other review articles complementing the approach presented here.  相似文献   

10.
We study the structure of shocks in clumpy media, using a multifluid formalism. As expected, shocks broaden as they weaken: for sufficiently weak shocks, no viscous subshock appears in the structure. This has significant implications for the survival of dense clouds in regions overrun by shocks in a wide range of astrophysical circumstances, from planetary nebulae to the nuclei of starburst galaxies.  相似文献   

11.
It is shown that the planetary nebulae can be divided into three types according to the values of the mass of shell and a central star. The criteria are given using which one can determine the mass type of the nebula. The distance scale of each mass-type planetary nebulae is given. The distribution of planetary nebulae in the Galaxy, their formation rate, scale-height and other physical and kinematic characteristics are investigated. A catalogue of planetary nebulae emitting in the radio range is given.  相似文献   

12.
In this paper we gauge the potentiality of Gaia in the distance scale calibration of planetary nebulae (PNe) by assessing the impact of DR1 parallaxes of central stars of Galactic PNe (CSPNe) against known physical relations. For selected PNe targets with state-of-the-art data on angular sizes and fluxes, we derive the distance-dependent parameters of the classical distance scales, i.e., physical radii and ionized masses, from DR1 parallaxes; we propagate the uncertainties in the estimated quantities and evaluate their statistical properties in the presence of large relative parallax errors; we populate the statistical distance scale diagrams with this sample and discuss its significance in light of existing data and current calibrations. We glean from DR1 parallaxes 8 CSPNe with S/N> 1. We show that this set of potential calibrators doubles the number of extant trigonometric parallaxes (from HST and ground-based), and increases by two orders of magnitude the domain of physical parameters probed previously. We then use the combined sample of suitable trigonometric parallaxes to fit the physical-radius-to-surface-brightness relation. This distance scale calibration, although preliminary, appears solid on statistical grounds, and suggestive of new PNe physics. With the tenfold improvement in PNe number statistics and astrometric accuracy expected from future Gaia releases the new distance scale, already very intriguing, will be definitively constrained.  相似文献   

13.
Any calibration of the present value of the Hubble constant (H 0) requires recession velocities and distances of galaxies. While the conversion of observed velocities into true recession velocities has only a small effect on the result, the derivation of unbiased distances which rest on a solid zero point and cover a useful range of about 4–30 Mpc is crucial. A list of 279 such galaxy distances within v < 2,000 km s−1 is given which are derived from the tip of the red-giant branch (TRGB), from Cepheids, and/or from supernovae of type Ia (SNe Ia). Their random errors are not more than 0.15 mag as shown by intercomparison. They trace a linear expansion field within narrow margins, supported also by external evidence, from v = 250 to at least 2,000 km s−1. Additional 62 distant SNe Ia confirm the linearity to at least 20,000 km s−1. The dispersion about the Hubble line is dominated by random peculiar velocities, amounting locally to <100 km s−1 but increasing outwards. Due to the linearity of the expansion field the Hubble constant H 0 can be found at any distance >4.5 Mpc. RR Lyr star-calibrated TRGB distances of 78 galaxies above this limit give H 0 = 63.0 ± 1.6 at an effective distance of 6 Mpc. They compensate the effect of peculiar motions by their large number. Support for this result comes from 28 independently calibrated Cepheids that give H 0 = 63.4 ± 1.7 at 15 Mpc. This agrees also with the large-scale value of H 0 = 61.2 ± 0.5 from the distant, Cepheid-calibrated SNe Ia. A mean value of H 0 = 62.3 ± 1.3 is adopted. Because the value depends on two independent zero points of the distance scale its systematic error is estimated to be 6%. Other determinations of H 0 are discussed. They either conform with the quoted value (e.g. line width data of spirals or the D n −σ method of E galaxies) or are judged to be inconclusive. Typical errors of H 0 come from the use of a universal, yet unjustified P–L relation of Cepheids, the neglect of selection bias in magnitude-limited samples, or they are inherent to the adopted models.  相似文献   

14.
本文发表的是用北京天文台60厘米施密特望远镜进行发射线星系物端棱镜巡天结果的第四篇文章。文中的表1包括100个发射线天体,其中的96个是发射线星系;其余的对象有3个行星状星云,1个发射线星。在这些发射线星系中,属于s,sd型的有69个,d,ds型的有27个,分别占72％和28％。除了4个已知的Seyfert星系之外,至少还有5个也可能是Seyfert星系。这些发射线天体中的23个是IRAS源,它们都与具有强发射的现象相联系.  相似文献   

15.
There are about 50 galactic planetary nebulae know to have [WR] type nuclei. We have compared their nebular properties with those of the other planetary nebulae in the Galaxy. We have found that the nebular morphological types are similarly distributed in the two groups. Bipolar nebulae constitute only 20% of the total in each group. The distribution of the nebular electron densities and abundance ratios N/O, He/H and C/O are the same in the two groups. The only marked difference is that nebular expansion velocities are larger in the group of planetary nebulae with [WR] central stars. We argue that the WR phenomenon does not preferentially occur in more massive central stars of planetary nebulae, contrary to what has been suggested in some former studies. We demonstrate that, for most of the observed [WR] type objects, the WR phenomenon cannot be triggered by a late helium shell flash event.The results of our investigation are published inAstronomy & Astrophysics 303, 893 (1995) and in the proceedings of the 2nd International Colloquium on Hydrogen-deficient Stars, C.S. Jeffery & U. Heber (eds), Astronomical Society of the Pacific Conference Series, Vol. 96, p. 209 (1996).  相似文献   

16.
The local expansion field (v 220 <1200 km s-1) and the cosmic expansion field out to 30 000 km s-1 are characterized by H 0 = 58 [km s-1 Mpc-1]. While the random error of this determination is small (± 2 units), it may still be affected by systematic errors as large as ±10%>. The local expansion is outlined by Cepheids and by Cepheid-calibrated TF distances of a complete sample of field galaxies and by nearby groups and clusters; the cosmic expansion is defined by Cepheid-calibrated SNe Ia. The main source of systematic errors are therefore the shape and the zero point of the P-L relation of Cepheids and its possible dependence on metallicity. GAIA will essentially eliminate these systematic error sources. Another source of systematic error is due to the homogenization of SNe Ia as to decline rate Δm 15 and color (B-V). GAIA will discover most of the 1100 SNe Ia within 10 000 km s-1, which will occur during its four-year lifetime. If their photometric parameters can be determined from the ground, they will fix the dependence of the SNe Ia luminosity on Δ m 15 and (B-V) with high accuracy. At the same time they will yield exquisite distances to an equal number of field galaxies. – GAIA will also revolutionize the very local distance scale by determining fundamental distances of the companion galaxies of the Milky Way and even of some spirals in- and possibly outside the Local Group from their rotation curves seen in radial velocities and proper motions. Moreover, GAIA will obtain trigonometric parallaxes of RR Lyrae stars, of red giants defining the TRGB, of stars on the ZAMS, of White Dwarf defining their cooling sequence, and of globular clusters, and determine the metallicity dependence of these distance indicators. It will thus establish a self-controlling network of distance indicators within the Local Group and beyond. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

17.
The location of the lower Main Sequence in the Colour Magnitude Diagram, the magnitude of the Red Clump and the magnitude of the tip of the Red Giant Branch are three popular stellar distance indicators. With the present observational capabilities they can be applied to reach distances ranging from the Galactic Disk and Halo populations, to galaxies beyond the Local Group. The techniques devised to exploit these distance indicators are presented, together with a discussion of their calibration, the main sources of systematic errors and the predicted impact of the results from the GAIA mission.  相似文献   

18.
We present new Planetary Nebula Spectrograph observations of the ordinary elliptical galaxy NGC 4494, resulting in positions and velocities of 255 planetary nebulae out to seven effective radii (25 kpc). We also present new wide-field surface photometry from MMT/Megacam, and long-slit stellar kinematics from VLT/FORS2. The spatial and kinematical distributions of the planetary nebulae agree with the field stars in the region of overlap. The mean rotation is relatively low, with a possible kinematic axis twist outside  1 R e  . The velocity dispersion profile declines with radius, though not very steeply, down to  ∼70 km s−1  at the last data point.
We have constructed spherical dynamical models of the system, including Jeans analyses with multi-component Λ cold dark matter (CDM) motivated galaxies as well as logarithmic potentials. These models include special attention to orbital anisotropy, which we constrain using fourth-order velocity moments. Given several different sets of modelling methods and assumptions, we find consistent results for the mass profile within the radial range constrained by the data. Some dark matter (DM) is required by the data; our best-fitting solution has a radially anisotropic stellar halo, a plausible stellar mass-to-light ratio and a DM halo with an unexpectedly low central density. We find that this result does not substantially change with a flattened axisymmetric model.
Taken together with other results for galaxy halo masses, we find suggestions for a puzzling pattern wherein most intermediate-luminosity galaxies have very low concentration haloes, while some high-mass ellipticals have very high concentrations. We discuss some possible implications of these results for DM and galaxy formation.  相似文献   

19.
HST WFPC2 observations of Cepheids in M96 (NGC 3368) are used to find a distance to that galaxy of 11.2±1.0  Mpc. This estimate is based on a calibration of the Cepheid period–luminosity relation in the Large Magellanic Cloud, and includes a correction for the difference in metallicity between the two systems. There are good reasons for believing M96 is at the same distance as four E/S0 galaxies in the Leo-I group, and hence we calibrate secondary distance indicators based on the early-type galaxies, namely the fundamental plane and surface-brightness-fluctuation method. Also the Type Ia supernova 1998bu occurred in M96 itself and is used to calibrate the SN Ia distance scale. These methods reach to recession velocities of greater than 5000 km s−1 and can therefore allow us to evaluate the Hubble constant without reference to the peculiar velocity of M96 itself. In fact, these indicators agree well between themselves and hence we find H 0=67±7 km s−1 Mpc−1 where the quoted error includes estimates of potential systematic effects.  相似文献   

20.
金属丰度是表征星系特征的重要参量,对于理解星系的形成与演化具有重要意义。随着观测设备的不断完善与发展,已经获得越来越多的星系(包括近邻星系、中等红移及高红移星系)金属丰度的观测资料。在光致电离模型方面也取得了很大进展．这些对于理解星系中金属及恒星成分的累积历史有非常重要的作用。有多种方法可以用来估计星系的金属丰度(主要是星际介质中气相的O丰度),介绍和评述了估计星系的O丰度的多种方法,包括电子温度的方法、R23方法以及其他一些“强线”比值的方法,并给出了相应的解析公式,同时介绍了电离星云的物理本质及由光致电离模型估计星系金属丰度的方法,还给出了估计星系的C和N元素丰度的方法。  相似文献   

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