Article

Nuclei prompt stellar rethink

December 2001
Physics World 14(12):23-24

December 2001
14(12):23-24

DOI:10.1088/2058-7058/14/12/26

Authors:

During the last century great strides were made in understanding the structure of the universe and the overall processes that drive its evolution. The utter vastness of the cosmos became apparent following the discovery that although our own galaxy is gigantic, it is just one of many billions of galaxies scattered throughout the universe. The sheer physical size of the universe makes it even more remarkable that the evolution of galaxies is directly linked to physical processes that occur on the smallest scales – the reactions between atomic nuclei.

ResearchGate has not been able to resolve any citations for this publication.

ResearchGate has not been able to resolve any references for this publication.

Article

Full-text available

Detection of a new, low-brightness supernova remnant possibly associated with EGRET sources

March 2001 · Astronomy and Astrophysics

We report on the discovery of a shell-type supernova remnant in the southern sky. It is a large (8*8), low-brightness source with a nonthermal radio spectrum, which requires background filtering to isolate it from the diffuse background emission of the Galaxy. Three 3EG gamma-ray sources are spatially correlated with the radio structure. We have made 21-cm line observations of the region and ... [Show full abstract] found that two of these sources are coincident with HI clouds. We propose that the gamma-ray emission is the result of hadronic interactions between high-energy protons locally accelerated at the remnant shock front and atomic nuclei in the ambient clouds. Comment: 6 pages, 5 figures

Article

Dynamics in the Centres of Triaxial Elliptical Galaxies

January 1987 · Proceedings of the International Astronomical Union

Ortwin Gerhard

Three kinds of deviations from a homogeneous core which occur in triaxial elliptical galaxies are discussed: (1) a central point mass with a typical mass of 100 million solar masses, (2) a dense but extended central star cluster such as that inferred for M31, and (3) central cusps. A box orbit scattering model used to describe the first two of these deviations is discussed. The effect of box ... [Show full abstract] orbit scattering on the galaxy is addressed, and the orbit structure of central density cusps is examined. The observable consequences of black holes or dense star clusters are considered.

Article

Full-text available

The Theorem of the Definite life of one Galaxy in the Universe i.e. the Cosmos

September 2017

Dhananjay Shantaram Janorkar

The Theorem of the Evolution or Creation of the Universe i.e. the Cosmos and the Speed, [Wishavachi Mhananjech Bramhandachi Uttapathi Kinuva Nirmiti Va Vegacha Shidhanta, (In Marathi)], The Theorem of the Volume (Extent) of the Solar System – 2015 (Revise Research Paper - 2016), [Surya malecha Vyapacha Shidhanta - 2015 (Sudharalela Sanshodhan Paper - 2016) (In Marathi)], The theorem with respect ... [Show full abstract] to the total number of solar systems in the galaxy, the total number of planets revolving around the sun and having earth like organisms and the definite volume (extent) of the galaxy, [Aakashagange Madhil Yekun Surya Mala, Aakashagange Madhil Suryaa Bhowati Phiranare Pruthavi Pramane Jivan Srushati Aasalele Graha Aani Aakashagangechya Nichit Vyapacha Shidhanta, (In Marathi)], The theorem with respect to the total numbers of Planets - Stars, Mass and Holes (Hollow part like Hole or Space), Solar Systems, Planets revolving around the sun and having earth like organisms, Galaxies in the Cosmos i.e., Universe and the definite Volume (Extent) of the Cosmos i.e., Universe, [Wishava Madhil Mhangech Bramhanda Madhil Yekun Graha – Tare - Vastuman Aani Pokalya (Pokali Sarakha Pokal Bhag Kiuvha Aavkash), Surya Mala, Suryabhowati Phirnare Pruthavi Pramane Jivan Srushati Aaslele Grah, Aakashaganga Aani Wishavachya Mhananjech Bramhandachya Nichit Vyapacha Shidhanta, (In Marathi)], While studying deeply and putting them before the world and researching the paper for the same, it came to my notice that if everything is definite, then the life of Galaxy in the Universe i.e. the Cosmos should also be definite. From this theorem, I noticed, The Theorem of the definite life of one Galaxy in the Universe i.e. the Cosmos, [Vishva Mhanajech Bramhanda Madhil, Eka Akasagangeche Nishit Ayushacha Siddhanta, (In Marathi)], and I have tried to put this research paper in scientific and mathematical language in a clear manner. In this research paper, there is nothing indefinite, approximate or imaginary, everything is definite. In Geometry, symbol for measurement accepted by world scientists (world official) is degree and the very degree is the root, scale, source and base of the research. Degree: Closed chop (Compass), Tip of the compass means point, means 1 point, means 1º degree, means dot • = degree means unit of measurement. The base of this whole research is 36º measure of circle.

Article

Full-text available

A Parsec-Scale Accelerating Radio Jet in the Giant Radio Galaxy NGC 315

January 2009 · The Astrophysical Journal

Observations of the core of the giant radio galaxy NGC 315 made with VLBI interferometers are discussed in the context of a relativistic jet. The sidedness asymmetry suggests Doppler favoritism from a relativistic jet. The presence of moving features in the jet, as well as jet counterjet brightness ratios, hint at an accelerating, relativistic jet. An increasing jet velocity is also supported by ... [Show full abstract] a comparison of the jet's observed properties with the predictions of an adiabatic expansion model. On the parsec scale, the jet is unpolarized at a wavelength of 6 cm to a very high degree, in clear distinction to the high polarization seen on the kiloparsec scale.

Article

Phat ELVIS: The inevitable effect of the Milky Way’s disc on its dark matter subhaloes

August 2019 · Monthly Notices of the Royal Astronomical Society

We introduce an extension of the ELVIS project to account for the effects of the Milky Way galaxy on its subhalo population. Our simulation suite, Phat ELVIS, consists of 12 high-resolution cosmological dark matter-only (DMO) zoom simulations of Milky Way-size ΛCDM haloes [M_v = (0.7−2) × 10^(12) M⊙] along with 12 re-runs with embedded galaxy potentials grown to match the observed Milky Way disc ... [Show full abstract] and bulge today. The central galaxy potential destroys subhalos on orbits with small pericentres in every halo, regardless of the ratio of galaxy mass to halo mass. This has several important implications. (1) Most of the Discruns have no subhaloes larger than V_(max) = 4.5 km s^(-1) within 20 kpc and a significant lack of substructure going back ∼8 Gyr, suggesting that local stream-heating signals from dark substructure will be rare. (2) The pericentre distributions of Milky Way satellites derived from Gaia data are remarkably similar to the pericentre distributions of subhaloes in the Disc runs, while the DMO runs drastically overpredict galaxies with pericentres smaller than 20 kpc. (3) The enhanced destruction produces a tension opposite to that of the classic ‘missing satellites’ problem: in order to account for ultra-faint galaxies known within 30 kpc of the Galaxy, we must populate haloes with V_(peak) ≃ 7 km s^(-1)(M ≃ 3 × 10^7 M⊙ at infall), well below the atomic cooling limit of V_(peak)≃16kms^(-1) (M ≃ 5 × 10^8M⊙ at infall). (4) If such tiny haloes do host ultra-faint dwarfs, this implies the existence of ∼1000 satellite galaxies within 300 kpc of the Milky Way.

Article

Stars, Galaxies, Cosmos: The Past Decade, the Next Decade

August 1980 · Science

V. C. Rubin

Our perception of the universe has been altered by recent discoveries in astronomy, discoveries of new objects and of new phenomena, coming from a wide range of observing techniques. By 1990 astronomers expect to know more about the distribution of mass in the universe, the physics of energetic sources, and the intricate interconnections of astrophysical processes on a variety of spatial and ... [Show full abstract] temporal scales.

Chapter

The Role of Galaxy Stellar Mass in the Colour–Density Relation up to z ~ 1

July 2011

It is well known that galaxy properties correlate with the local environment in which galaxies reside. In contrast, it is still matter of debate why and when these environmental dependences originate, and whether only one “main” property depends on environment, thus driving all the others environmental dependences via the correlations among properties themselves. We use the first ∼ 10, 000 ... [Show full abstract] spectra of the zCOSMOS sample (I ≤ 22. 5) to study the role of galaxy stellar mass in the colour–density relation up to z = 1. We confirm that within a luminosity-limited sample (M B ≤ − 20. 5 − z) red galaxies reside mainly in high densities (δ) at least up to z = 1. This trend becomes weaker for increasing redshifts, and it is mirrored by the Dn 4, 000 \r{A} break–density relation. We also find that up to z ∼ 1 the fraction of galaxies with log(EW[OII]) ≥ 1. 15 is higher for lower δ. Given the triple dependence among galaxy colours, stellar mass and δ, the colour–δ relation that we find can be due to the broad range of stellar masses embedded in the sample. We find that once mass is fixed the colour-δ relation is globally flat up to z ∼ 1 for galaxies with log(M ∕ M sun ) ≥ 10. 7. On the contrary, even at fixed mass we observe that within 0. 1 ≤ z ≤ 0. 5 the fraction of red galaxies with log(M ∕ M sun ) ≤ 10. 7 depends on δ. We suggest a scenario in which the colour depends primarily on stellar mass, but for an intermediate mass regime (10. 2 ≤ log(M ∕ M sun ) ≤ 10. 7) the local density modulates this dependence. These lower mass galaxies formed more recently, in an epoch when evolved structures were already in place, and their longer SFH allowed environment-driven physical processes to operate during longer periods of time.

Chapter

The Cosmos, The Sun and The Earth

July 2016

Robert U. Ayres

Parts of this could logically be included in Chap. 3 under Ideas. However, the story of ideas underlying current theories of cosmology are too complex to reduce to a few names and dates, although I will start with one. For most modern astronomers, the logical starting point of modern cosmology was Vesto Slipher’s discovery (1912) of the “red shift” (Z) of the in absorption lines for hydrogen (and ... [Show full abstract] other elements) in starlight from distant galaxies. The red shift, toward the infra-red part of the spectrum, indicates slightly lower frequencies (longer wavelengths). It can be explained in terms of relative motion, like the “Doppler effect”. (The Doppler effect is what makes the sound of an approaching siren a little higher in pitch than the sound of a siren moving away). By 1920, 36 of 41 galaxies for which data had been obtained, were seen to be moving away from our galaxy, the Milky Way. Current data puts the fraction much higher.

Article

Full-text available

HIPASS detection of an intergalactic gas cloud in the NGC 2442 group

December 2008 · The Astrophysical Journal

We report the discovery from the H I Parkes All-Sky Survey (HIPASS) of a gas cloud associated with the asymmetric spiral galaxy NGC 2442. This object, designated HIPASS J0731-69, contains ~109 M☉ of H I, or nearly one-third as much atomic gas as NGC 2442 itself. No optical counterpart to any part of HIPASS J0731-69 has yet been identified, consistent with the gas being diffuse and its streamlike ... [Show full abstract] kinematics. If the gas in HIPASS J0731-69 was once part of NGC 2442, then it was most likely a fairly recent tidal encounter with a moderately massive companion that tore it loose, although the possibility of ram-pressure stripping cannot be ruled out. This discovery highlights the potential of the HIPASS data for yielding new clues to the nature of some of the best-known galaxies in the local universe.

Conference Paper

Wolf-Rayet galaxies at many radio wavelengths and H alpha: radio super-star-clusters

January 1999 · Symposium - International Astronomical Union

We have observed nine Wolf-Rayet galaxies at 20,6, 3.6 and 2 cm from the VLA and at Halpha from the Wise Observatory, and have mapped the radio spectral index in each galaxy on sub-arcsec scales. We find that more than half the WR sample has distinct regions where the radio spectrum rises between 6 and 2 cm. We believe that this is the radio signature of the youngest super-star-clusters which are ... [Show full abstract] otherwise invisible, and which require N-Lyc greater than or equal to 10(52), or equivalent to 750 stars of the O7 subtype. We call these sources radio superstar-clusters.

Article

Full-text available

Warped diffusive radio halo around the quiescent spiraledge-on galaxy NGC 4565

July 2019 · Astronomy and Astrophysics

Context . Cosmic rays play a pivotal role in launching galactic winds, particularly in quiescently star-forming galaxies where the hot gas alone is not sufficient to drive a wind. Except for the Milky Way, not much is known about the transport of cosmic rays in galaxies. Aims . In this Letter, we present low-frequency observations of the nearby edge-on spiral galaxy NGC 4565 using the ... [Show full abstract] LOw-Frequency ARray (LOFAR). With our deep 144 MHz observations, we obtain a clean estimate of the emission originating from old cosmic-ray electrons (CRe), which is almost free from contamination by thermal emission. Methods . We measured vertical profiles of the non-thermal radio continuum emission that we fitted with Gaussian and exponential functions. The different profile shapes correspond to 1D cosmic-ray transport models of pure diffusion and advection, respectively. Results . We detect a warp in the radio continuum that is reminiscent of the previously known H I warp. Because the warp is not seen at GHz-frequencies in the radio continuum, its minimum age must be about 100 Myr. The warp also explains the slight flaring of the thick radio disc that can otherwise be well described by a Gaussian profile with an FWHM of 65 arcsec (3.7 kpc). Conclusions . The diffusive radio halo together with the extra-planar X-ray emission may be remnants of enhanced star-forming activity in the past where the galaxy had a galactic wind, as GHz-observations indicate only a weak outflow in the last 40 Myr. NGC 4565 could be in transition from an outflow- to an inflow-dominated phase.

Article

Interstellar medium in nearby elliptical radio galaxies

January 2010

Breezy Ocaña Flaquer

Incluye Resumen y Conclusiones escritos en inglés y español Tesis Univ. Granada. Departamento de Física Teórica y del Cosmos. Leída el 9 de abril de 2010