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Post Info TOPIC: NGC 5044 and 4636


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Title: Dynamics of the NGC 4636 globular cluster system II. Improved constraints from a large sample of globular cluster velocities
Authors: Ylva Schuberth, Tom Richtler, Michael Hilker, Ricardo Salinas, Boris Dirsch, Soeren S. Larsen

We present new radial velocities for 289 globular clusters around NGC 4636, the southernmost giant elliptical galaxy of the Virgo cluster. The data were obtained with FORS2/MXU at the Very Large Telescope. Together with data analysed in an earlier study (Schuberth et al. 2006), we now have a sample of 460 globular cluster velocities out to a radius of 12 arcmin (60 kpc) available - one of the largest of its kind. This new data set also provides a much more complete angular coverage. Moreover, we present new kinematical data of the inner stellar population of NGC 4636. We perform an updated Jeans analysis, using both stellar and GC data, to better constrain the dark halo properties. We find a stellar M/L-ratio of 5.8 in the R-band, higher than expected from single stellar population synthesis. We model the dark halo by cored and cuspy analytical halo profiles and consider different anisotropies for the tracer populations. Properties of NFW halos lie well within the expected range of cosmological simulations. Cored halos give central dark matter densities, which are typical for elliptical galaxies of NGC 4636's luminosity. The surface densities of the dark matter halos are higher than those of spiral galaxies. We compare the predictions of Modified Newtonian Dynamics with the derived halo properties and find satisfactory agreement. Therefore NGC 4636 therefore falls onto the baryonic Tully-Fisher relation for spiral galaxies. The comparison with the X-ray mass profile of Johnson et al. (2009) reveals satisfactory agreement only, if the abundance gradient of hot plasma has been taken into account. This might indicate a general bias towards higher masses for X-ray based mass profiles in all systems, including galaxy clusters, with strong abundance gradients.

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Title: Suzaku Observation of the Metallicity Distribution in the Elliptical Galaxy NGC 4636
Authors: Katsuhiro Hayashi (1), Yasushi Fukazawa (1), Miyako Tozuka (1), Sho Nishino (1), Kyoko Matsushíta (2), Yoh Takei (3), Keith A. Arnaud (4 and 5) ((1)Department of Physical Science, Hiroshima University (2)Department of Physics Tokyo University of Science (3)Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA) (4)CRESST and X-ray Astrophysics Laboratory, NASA Goddard Flight Space Centre (5)Astronomy Department, University of Maryland)

NGC 4636, an X-ray bright elliptical galaxy, was observed for 70 ks with Suzaku. The low background and good energy resolution of the XIS enable us to estimate the foreground Galactic emission accurately and hence measure, for the first time, the O, Mg, Si and Fe abundances out to a radius of ~28 arcmin (\simeq 140 kpc). These metal abundances are as high as >1 solar within the central 4' and decrease by ~50% towards the outer regions. Further, the O to Fe abundance ratio is about 0.60--1.0 solar in all regions analysed, indicating that the products of both SNe II and SNe Ia have mixed and diffused to the outer regions of the galaxy. The O and Fe metal mass-to-light-ratios (MLR) of NGC 4636 are 2--3 times larger than those of NGC 1399 implying that metal distributions in NGC 4636 are less extended than those in NGC 1399, possibly due to environmental factors, such as frequency of galaxy interaction. We also found that the MLRs of NGC 4636 at 0.1 r_{180} are ~5 times smaller than those of clusters of galaxies, possibly consistent with the correlation between temperature and MLR of other spherically symmetric groups of galaxies. We also confirmed a resonant scattering signature in the Fe_{XV II}} line in the central region, as previously reported using the XMM-Newton RGS.

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Do Supermassive Black Holes Stunt Stellar Birth in Galaxies?

New evidence from NASA's Spitzer Space Telescope shows that supermassive black holes at the centres of elliptical galaxies keep the galactic "thermostat" so high gas cannot cool, stunting the birth of new stars.
For the first time ever, astronomers have detected dust grains mingling with blazing hot gas at temperatures of 10 million degrees Kelvin (about 10 million degrees Celsius, or 17 million degrees Fahrenheit), in an area surrounding the elliptical-shaped galaxy called NGC 5044. Scientists hope this new finding will provide insight into how supermassive black holes reduce the stellar fertility in elliptical galaxies by heating gas.

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Title: Spitzer Observations of Transient, Extended Dust in Two Elliptical Galaxies: New Evidence of Recent Feedback Energy Release in Galactic Cores
Authors: Pasquale Temi, Fabrizio Brighenti, William G. Mathews

Spitzer observations of extended dust in two optically normal elliptical galaxies provide a new confirmation of buoyant feedback outflow in the hot gas atmospheres around these galaxies. AGN feedback energy released near central supermassive black holes is required to prevent wholesale cooling and (unobserved) star formation in group and cluster-centred elliptical galaxies. In NGC 5044 we observe interstellar (presumably PAH) emission at 8 microns out to about 5 kpc and both NGC 5044 and 4636 contain similarly extended cold dust emitting at 70 microns in excess of that expected from stellar mass loss. This is significant since the lifetime of dust in the hot ~1keV interstellar gas by sputtering destruction, ~10^7 yrs, establishes the time when the dust first entered the hot gas. We argue that the extended dust originated in dusty disks or clouds in the galactic core that were disrupted, heated and buoyantly transported out into the hot gas. The mass of excess extended dust,~10^5 Msol, is comparable to dust masses estimated in optically obscuring dust clouds and disks observed in the cores of many elliptical galaxies. However, the central dust in NGC 5044 and 4636 has been disrupted into many small filaments. Most dramatically, we show that NGC 5044 has asymmetrically extended interstellar dust-related 8 micron emission that is spatially coincident with extended Halpha+[NII] emission from warm gas. A calculation shows that dust-assisted cooling in buoyant hot gas moving out from the core of NGC 5044 can cool the gas within a few kpc in about ~10^7 yrs, explaining the optical line emission observed. Furthermore, X-ray data in both galaxies are unusual in indicating recent or ongoing dynamic activity presumably associated with feedback energy released from the central black hole.

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