Global HI profiles of spiral galaxies

In this paper we present short HI synthesis observations of 57 galaxies without HI information in the RC3. These are a by-product of a large survey with the WSRT of the neutral hydrogen gas in spiral and irregular galaxies. Global profiles and related quantities are given for the 42 detected galaxies and upper limits for the remaining 15. A number of galaxies have low values of HI mass-to-blue luminosity ratio.Comment: A LATEX file without figures. The postscript version including all the figures can be retrieved from http://www.astro.rug.nl:80/~secr/ Accepted for publication in Astronomy & Astrophysics Suppl. Serie

The blazar-like radio structure of the TeV source IC310

Context. The radio galaxy IC310 in the Perseus cluster has recently been detected in the gamma-ray regime at GeV and TeV energies. The TeV emission shows time variability and an extraordinarily hard spectrum, even harder than the spectrum of the similar nearby gamma-ray emitting radio galaxy M87. Aims. High-resolution studies of the radio morphology help to constrain the geometry of the jet on sub-pc scales and to find out where the high-energy emission might come from. Methods. We analyzed May 2011 VLBA data of IC310 at a wavelength of 3.6 cm, revealing the parsec-scale radio structure of this source. We compared our findings with more information available from contemporary single-dish flux density measurements with the 100-m Effelsberg radio telescope. Results. We have detected a one-sided core-jet structure with blazar-like, beamed radio emission oriented along the same position angle as the kiloparsec scale radio structure observed in the past by connected interferometers. Doppler-boosting favoritism is consistent with an angle of theta < 38 degrees between the jet axis and the line-of-sight, i.e., very likely within the boundary dividing low-luminosity radio galaxies and BL Lac objects in unified schemes. Conclusions. The stability of the jet orientation from parsec to kiloparsec scales in IC310 argues against its classification as a headtail radio galaxy; i.e., there is no indication of an interaction with the intracluster medium that would determine the direction of the tail. IC310 seems to represent a low-luminosity FRI radio galaxy at a borderline angle to reveal its BL Lac-type central engine.Comment: 5 pages, 3 figures (1 color); A&A, accepte

A small X-ray corona of the narrow-angle tail radio galaxy NGC 1265 soaring through the Perseus cluster

A deep Chandra observation of NGC 1265 (3C 83.1B), the prototype for the narrow-angled-tailed (NAT) radio galaxy, reveals a small cool X-ray thermal corona (~ 0.6 keV) embedded in the hot ICM of the Perseus cluster (~ 6.7 keV). The corona is asymmetric with a sharp edge (~ 2.2'', or 0.8 kpc from the nucleus) to the south and an extension to the north (at least ~ 8'' from the nucleus), which is interpreted as the action of ram pressure while solely the static ICM confinement is unable to explain. We estimate that the corona is moving with a velocity of ~ 2.4 - 4.2 times the local sound speed to the south. The presence of the sharp edge for this small corona indicates that the transport processes are largely suppressed by the magnetic field there. The magnetic field around the corona also suppresses heat conduction by at least a factor of ~ 60 across the corona boundary. We conclude that it is unrealistic to study the interaction of the small X-ray coronae with the hot ICM without the consideration of the roles that magnetic field plays, a factor not included in current simulations. An absorbed (N_H=1.5-3x10^22 cm^-2) nucleus is also detected, which is not usual for FR I radio galaxies. Weak X-ray emission from three inner radio knots in the jets is also detected. Indentations at the east and west of the corona indicate interaction between the jets and the X-ray corona. Narrow jets carry great amounts of energy out of the central AGN and release the energy outside the corona, preserving the tiny and vulnerable corona. This case reveals that the inner kpc core of the corona of massive galaxies can survive both high-speed stripping and powerful AGN feedback. Thus, the cooling of the X-ray coronae potentially provides fuel to the central SMBH in rich environments where the amount of the galactic cold gas is at a minimum.Comment: revised version, 11 pages, 4 figures, emulateapj5.sty, accepted by ApJ, for the version with high-resolution figures (http://hea-www.harvard.edu/~msun/n1265.ps

Very high-energy gamma-ray emission from IC 310

We construct a systematic survey of extragalactic \gamma-ray sky at the energies above 100 GeV using the data of Fermi telescope. Such survey has not been previously done by the ground-based Cherenkov gamma-ray telescopes which have, contrary to Fermi, narrow field of view. We study a map of arrival directions of the highest energy photons detected by Fermi at Galactic latitudes |b| > 10 degrees and search for significant point source like excesses above the diffuse Galactic and extragalactic \gamma-ray backgrounds. We identify eight significant point source like excesses in this map. Seven of the eight sources are known TeV blazars. The previously unknown source is identified with a head-tail radio galaxy IC 310, situated in Perseus cluster of galaxies. The source is detected with significance 6 sigma above 30 GeV. We identify two possible scenaria for gamma-ray emission from this source. One possibility is that emission originates from the base of relativistic outflow from the active nucleus, as in the BL Lacs and FR I type radio galaxies. Otherwise gamma-ray photons could be produced at the bow shock formed in result of fast motion of the galaxy through the intracluster medium. The two models could be distinguished via the study of variability of the \gamma-ray signal.Comment: 4 pages, 4 figure

Canonical Particle Acceleration in FRI Radio Galaxies

Matched resolution multi-frequency VLA observations of four radio galaxies are used to derive the asymptotic low energy slope of the relativistic electron distribution. Where available, low energy slopes are also determined for other sources in the literature. They provide information on the acceleration physics independent of radiative and other losses, which confuse measurements of the synchrotron spectra in most radio, optical and X-ray studies. We find a narrow range of inferred low energy electron energy slopes, n(E)=const*E^-2.1 for the currently small sample of lower luminosity sources classified as FRI (not classical doubles). This distribution is close to, but apparently inconsistent with, the test particle limit of n(E)=const*E^-2.0 expected from strong diffusive shock acceleration in the non-relativistic limit. Relativistic shocks or those modified by the back-pressure of efficiently accelerated cosmic rays are two alternatives to produce somewhat steeper spectra. We note for further study the possiblity of acceleration through shocks, turbulence or shear in the flaring/brightening regions in FRI jets as they move away from the nucleus. Jets on pc scales and the collimated jets and hot spots of FRII (classical double) sources would be governed by different acceleration sites and mechanisms; they appear to show a much wider range of spectra than for FRI sources.Comment: 16 figures, including 5 color. Accepted to Astrophysical Journa

Galaxy Populations and Evolution in Clusters II: Defining Cluster Populations

This paper presents quantitative techniques for studying, in an unbiased manner, the photometric and structural properties of galaxies in clusters, including a means to identify likely background objects in the absence of redshift information. We develop self-consistent and reproducible measurements of fundamental properties of galaxies such as radius, surface brightness, concentration of light and structural asymmetry. We illustrate our techniques through an application to deep UBR images, taken with the WIYN 3.5m telescope, of the central ~173 arcmin^2 (or 0.3 Mpc * 0.3 Mpc) of the cluster Abell 0146 (Perseus). Our techniques allow us to study the properties of the galaxy population in the center of Perseus down to M_B = -11. Using these methods, we describe and characterize a well-defined relation between absolute magnitude and surface brightness for galaxy cluster members across the entire range of galaxy luminosity from M_B = -20 to M_B = -11. The galaxies that are assigned by our techniques to the background show no such tight relationship between apparent magnitude and surface brightness, with the exception of those we identify as being members of a background cluster of galaxies at z ~ 0.55. We, however, find that at the fainter magnitudes, M_B > -16, there is a large scatter about the underlying color--magnitude relation defined by the brighter galaxies. Our analysis also indicates that the vast majority of Perseus galaxies are `normal', with little evidence for features associated with evolution; we however discuss the detailed properties of a handful of unusual galaxies. Finally, the galaxy luminosity function of the Perseus cluster center is computed, with a derived faint end slope of alpha = -1.44+/-0.04, similar to values found in other nearby clusters.Comment: Accepted on Feb. 2, 2002 to the Astronomical Journa

Multifrequency radio continuum observations of head-tail galaxies in the Perseus cluster

New observations of head-tail radio galaxies in the Perseus cluster at 21, 49 and 92 cm using the WSRT are presented. Two new head-tail galaxies were discovered bringing the total for the cluster to five. We show total intensity maps for all of them and spectral index distribution and polarization maps for NGC 1265 and IC 310. The observations with high dynamic range, obtained with the WSRT and the redundancy and self-calibration techniques, reveal a large extension of the tail of NGC 1265 both at 49 cm and at 92 cm. The projected tail bends over an angle of almost 360 degrees. There are several clear differences between the bright and the faint part of the radio tail: within a distance of one or two resolution beams the intensity decreases by more than an order of magnitude and the spectral index steepens from -1 to -2. The simplest model for the tail is that it delineates the orbit of the galaxy through the cluster. Because the tail is seen in projection, the faint part of the tail is visible only when it is not superimposed onto the bright part of the tail. It is likely, however, that large scale motions of the hot intracluster medium also help shape the tail. In this respect it is interesting to note that the tails of both NGC 1265 and IC 310, as well as the low brightness emission of NGC 1275 appear to have their faint extensions shifted to the east. The very long tail of NGC 1265 makes it possible to test at low frequencies models of the ageing process of the radiating electrons. In the faint part of the tail the brightness temperature is very low, which either indicates a very weak magnetic field or a large deviation from equipartition between particle and magnetic energy. The most remarkable properties of the faint part of the tail of NGC1265, namely its constant surface brightness and spectral index, are compared with three synchrotron ageing models, making some standard assumptions. All these models disagree with either the data or one of the assumptions. The Kardashev-Pacholczyk model and the Komissarov-Gubanov model require magnetic fields stronger than the equipartition value; the Jaffe-Perola model and the Komissarov-Gubanov model require an additional process, like in situ reacceleration or bulk streaming motions of electrons in the tail, far in excess of a plausible galaxy speed, to explain the observed spectra