Feedback Heating with Slow Jets in Cooling Flow Clusters

We propose a scenario in which a large fraction, or even most, of the gas cooling to low temperatures of T<10^4 K in cooling flow clusters, directly gains energy from the central black hole. Most of the cool gas is accelerated to non-relativistic high velocities, v ~ 10^3-10^4 km/sec, after flowing through, or close to, an accretion disk around the central black hole. A poorly collimated wind (or double not-well collimated opposite jets) is formed. According to the proposed scenario, this gas inflates some of the X-ray deficient bubbles, such that the average gas temperature inside these bubbles (cavities) in cooling flow clusters is kT_b ~< 100 keV. A large fraction of these bubbles will be very faint, or not detectable, in the radio. The bright rims of these weak smaller bubbles will appear as ripples. We suggest that the X-ray ripples observed in the Perseus cluster, for example, are not sound waves, but rather the rims of radio-faint weak bubbles which are only slightly hotter than their environment. This scenario is incorporated into the moderate cooling flow model; although not a necessary ingredient in that model, it brings it to better agreement with observations. In the moderate cooling flow model a cooling flow does exist, but the mass cooling rate is ~<10% of that in old versions of cooling flow models.Comment: The Astrophysical Journal, in pres

Translocation of a polymer chain driven by a dichotomous noise

We consider the translocation of a one-dimensional polymer through a pore channel helped by a motor driven by a dichotomous noise with time exponential correlation. We are interested in the study of the translocation time, mean velocity and stall force of the system as a function of the mean driving frequency. We find a monotonous translocation time, in contrast with the mean velocity which shows a pronounced maximum at a given frequency. Interestingly, the stall force shows a nonmonotonic behavior with the presence of a minimum. The influence of the spring elastic constant to the mean translocation times and velocities is also presented.Comment: 11 pages, 7 figure

Study of contamination of liquid oxygen by gaseous nitrogen First quarterly report, 1 Jul. - 30 Sep. 1964

Analytical model development for contamination study of liquid oxygen by gaseous nitroge

SMAUG: a new technique for the deprojection of galaxy clusters

This paper presents a new technique for reconstructing the spatial distributions of hydrogen, temperature and metal abundance of a galaxy cluster. These quantities are worked out from the X-ray spectrum, modeled starting from few analytical functions describing their spatial distributions. These functions depend upon some parameters, determined by fitting the model to the observed spectrum. We have implemented this technique as a new model in the XSPEC software analysis package. We describe the details of the method, and apply it to work out the structure of the cluster A1795. We combine the observation of three satellites, exploiting the high spatial resolution of Chandra for the cluster core, the wide collecting area of XMM-Newton for the intermediate regions and the large field of view of Beppo-SAX for the outer regions. We also test the validity and precision of our method by i) comparing its results with those from a geometrical deprojection, ii) examining the spectral residuals at different radii of the cluster and iii) reprojecting the unfolded profiles and comparing them directly to the measured quantities. Our analytical method yields the parameters defining the spatial functions directly from the spectra. Their explicit knowledge allows a straightforward derivation of other indirect physical quantities like the gravitating mass, as well as a fast and easy estimate of the profiles uncertainties.Comment: 24 pages, 11 figures, 3 tables; emulateapj; accepted for publication in the Astrophysical Journa

Using Magnetic Activity and Galactic Dynamics to Constrain the Ages of M Dwarfs

We present a study of the dynamics and magnetic activity of M dwarfs using the largest spectroscopic sample of low-mass stars ever assembled. The age at which strong surface magnetic activity (as traced by H-alpha) ceases in M dwarfs has been inferred to have a strong dependence on mass (spectral type, surface temperature) and explains previous results showing a large increase in the fraction of active stars at later spectral types. Using spectral observations of more than 40000 M dwarfs from the Sloan Digital Sky Survey, we show that the fraction of active stars decreases as a function of vertical distance from the Galactic plane (a statistical proxy for age), and that the magnitude of this decrease changes significantly for different M spectral types. Adopting a simple dynamical model for thin disk vertical heating, we assign an age for the activity decline at each spectral type, and thus determine the activity lifetimes for M dwarfs. In addition, we derive a statistical age-activity relation for each spectral type using the dynamical model, the vertical distance from the Plane and the H-alpha emission line luminosity of each star (the latter of which also decreases with vertical height above the Galactic plane).Comment: 8 pages, 5 figures, to appear in the proceedings of IAU 258: The Ages of Star

Study of contamination of liquid oxygen by gaseous nitrogen third quarterly progress report, 1 jan. - 31 mar. 1965

Contamination of liquid oxygen by gaseous nitroge

The serendipituous discovery of a short-period eclipsing polar in 2XMMp

We report the serendipituous discovery of the new eclipsing polar 2XMMp J131223.4+173659. Its striking X-ray light curve attracted immediate interest when we were visually inspecting the source products of the 2XMMp catalogue. This light curve revealed its likely nature as a magnetic cataclysmic variable of AM Herculis (or polar) type with an orbital period of ~92 min, which was confirmed by follow-up optical spectroscopy and photometry. 2XMMp J131223.4+173659 probably has a one-pole accretion geometry. It joins the group of now nine objects that show no evidence of a soft component in their X-ray spectra despite being in a high accretion state, thus escaping ROSAT/EUVE detection. We discuss the likely accretion scenario, the system parameters, and the spectral energy distribution.Comment: Accepted for publication in A&

Radiative cooling, heating and thermal conduction in M87

The crisis of the standard cooling flow model brought about by Chandra and XMM-Newton observations of galaxy clusters, has led to the development of several models which explore different heating processes in order to assess if they can quench the cooling flow. Among the most appealing mechanisms are thermal conduction and heating through buoyant gas deposited in the ICM by AGNs. We combine Virgo/M87 observations of three satellites (Chandra, XMM-Newton and Beppo-SAX) to inspect the dynamics of the ICM in the center of the cluster. Using the spectral deprojection technique, we derive the physical quantities describing the ICM and determine the extra-heating needed to balance the cooling flow assuming that thermal conduction operates at a fixed fraction of the Spitzer value. We assume that the extra-heating is due to buoyant gas and we fit the data using the model developed by Ruszkowski and Begelman (2002). We derive a scale radius for the model of $\sim 5$ kpc, which is comparable with the M87 AGN jet extension, and a required luminosity of the AGN of a $few \times 10^{42}$ erg s$^{-1}$, which is comparable to the observed AGN luminosity. We discuss a scenario where the buoyant bubbles are filled of relativistic particles and magnetic field responsible for the radio emission in M87. The AGN is supposed to be intermittent and to inject populations of buoyant bubbles through a succession of outbursts. We also study the X-ray cool component detected in the radio lobes and suggest that it is structured in blobs which are tied to the radio buoyant bubbles.Comment: 25 pages, 10 figures and 2 tables. Accepted for publication in Ap

Investigating the properties of AGN feedback in hot atmospheres triggered by cooling-induced gravitational collapse

Radiative cooling may plausibly cause hot gas in the centre of a massive galaxy, or galaxy cluster, to become gravitationally unstable. The subsequent collapse of this gas on a dynamical timescale can provide an abundant source of fuel for AGN heating and star formation. Thus, this mechanism provides a way to link the AGN accretion rate to the global properties of an ambient cooling flow, but without the implicit assumption that the accreted material must have flowed onto the black hole from 10s of kiloparsecs away. It is shown that a fuelling mechanism of this sort naturally leads to a close balance between AGN heating and the radiative cooling rate of the hot, X-ray emitting halo. Furthermore, AGN powered by cooling-induced gravitational instability would exhibit characteristic duty cycles (delta) which are redolent of recent observational findings: delta is proportional to L_X/sigma_{*}^{3}, where L_X is the X-ray luminosity of the hot atmosphere, and sigma_{*} is the central stellar velocity dispersion of the host galaxy. Combining this result with well-known scaling relations, we deduce a duty cycle for radio AGN in elliptical galaxies that is approximately proportional to M_{BH}^{1.5}, where M_{BH} is the central black hole mass. Outburst durations and Eddington ratios are also given. Based on the results of this study, we conclude that gravitational instability could provide an important mechanism for supplying fuel to AGN in massive galaxies and clusters, and warrants further investigation.Comment: Accepted for publication in MNRAS. 8 page

On the Nature of Feedback Heating in Cooling Flow Clusters

We study the feedback between heating and cooling of the intra-cluster medium (ICM) in cooling flow (CF) galaxies and clusters. We adopt the popular view that the heating is due to an active galactic nucleus (AGN), i.e. a central black hole accreting mass and launching jets and/or winds. We propose that the feedback occurs with the entire cool inner region (r <~ 5-30 kpc), where the non-linear over-dense blobs of gas with a density contrast >~2 cool fast and are removed from the ICM before experiencing the next major AGN heating event. We term this scenario "cold-feedback". Some of these blobs cool and sink toward the central black hole, while others might form stars and cold molecular clouds. We derive the conditions under which the dense blobs formed by perturbations might cool to low temperatures (T <~ 10^4 K), and feed the black hole. The main conditions are found to be: (1) An over-dense blob must be prevented from reaching an equilibrium position in the ICM: therefore it has to cool fast, and the density profile of the ambient gas should be shallow; (2) Non-linear perturbations are required: they might have chiefly formed by previous AGN activity; (3) The cooling time of these non-linear perturbations should be short relative to few times the typical interval between successive AGN outbursts. (4) The blobs should be magnetically disconnected from their surroundings, in order not to be evaporated by thermal conduction.Comment: Replaced wiht the version accepted by the Ap