The results of a CO line survey in central cluster galaxies with cooling flows are presented. Cold molecular gas is detected with the IRAM 30m telescope, through CO(1-0) and CO(2-1) emission lines in 6-10 among 32 galaxies. The corresponding gas masses are between 3 x 10 8 and 4 x 10 1 0 M O .. These results are in agreement with recent CO detections by Edge (2001). A strong correlation between the CO emission and the Ha luminosity is also confirmed. Cold gas exists in the center of cooling flow clusters and these detections may be interpreted as evidence of the long searched for very cold residual of the hot cooling gas.

/pdf/cold-molecular-gas-in-cooling-flow-clusters-of-galaxies-4sxldf1rhi.pdf

Cold molecular gas in cooling flow clusters of galaxies

Cold molecular gas has been recently detected in several cooling flow clusters of galaxies where huge optical nebulosities often stand. These optical filaments are tightly linked to the cooling flow and to the related phenomena, like the rising bubbles of relativistic plasma, fed by the radio jets. We present here a map in the CO(2-1) rotational line of the cold molecular gas associated with some Halpha filaments surrounding the central galaxy of the Perseus cluster: NGC 1275. The map, extending to about 50 kpc (135 arcsec) from the center of the galaxy, has been made with the 18-receiver array HERA, at the focus of the IRAM 30m telescope. Although most of the cold gas is concentrated to the center of the galaxy, the CO emission is also clearly associated to the extended filaments conspicuous in ionised gas and could trace a possible reservoir fueling the star formation there. Some of the CO emission is also found where the X-ray gas could cool down more efficiently: at the rims of the central X-ray cavity (where the hot gas is thought to have been pushed out and compressed by the central AGN expanding radio lobes). The CO global kinematics does not show any rotation in NGC 1275. The cold gas is probably a mixture of gas falling down on the central galaxy and of uplifted gas dragged out by a rising bubble in the intracluster medium. As recenlty suggested in other cluster cores, the cold gas peculiar morphology and kinematics argue for the picture of an intermittent cooling flow scenario where the central AGN plays an important role.

/pdf/cold-molecular-gas-in-the-perseus-cluster-core-association-so7z6dj1bw.pdf

Cold molecular gas in the Perseus cluster core - Association with X-ray cavity, Halpha filaments and cooling flow -

Cold molecular gas has recently been detected in several cooling flow clusters of galaxies containing huge optical nebula. These optical filaments are tightly linked to cooling flows and related phenomena, such as rising bubbles of relativistic plasma fed by radio jets. We present here a map, in the CO(2–1) rotational line, of the cold molecular gas associated with some of the Hα filaments surrounding the central galaxy of the Perseus cluster: NGC 1275. The map, extending to about 50 kpc (135 arcsec) from the center of the galaxy, has been made with the 18-receiver array HERA at the focus of the IRAM 30 m telescope. Although most of the cold gas is concentrated to the center of the galaxy, the CO emission is also clearly associated with the extended filaments conspicuous in ionised gas, and could trace a possible reservoir fueling the star formation there. Some of the CO emission is also found where the X-ray gas could cool down more efficiently at the rims of the central X-ray cavities (where the hot gas is thought to have been pushed out and compressed by the expanding radio lobes of the central AGN). The CO global kinematics do not show any rotation in NGC 1275. The cold gas is probably a mixture of gas falling down on the central galaxy and of uplifted gas dragged out by a rising bubble in the intracluster medium. As recently suggested in other cluster cores, the cold gas peculiar morphology and kinematics argue for the picture of an intermittent cooling flow scenario where the central AGN plays an important role.

/pdf/cold-molecular-gas-in-the-perseus-cluster-core-association-8umuywyyyd.pdf

Cold molecular gas in the Perseus cluster core - Association with X-ray cavity, Hα filaments and cooling flow

1.

The basic features of the globular cluster system of the Milky Way are summarized: the total population, subdivision of the clusters into the classic metal-poor and metal-rich components, and first ideas on formation models. The distance to the Galactic center is derived from the spatial distribution of the inner bulge clusters, giving R 0 = (8.1 ± 1.0) kpc.




2.

The calibration of the fundamental distance scale for globular clusters is reviewed. Different ways to estimate the zero point and metallicity dependence of the RR Lyrae stars include statistical parallax and Baade-Wesselink measurements of field RR Lyraes, astrometric parallaxes, white dwarf cluster sequences, and field subdwarfs and main sequence fitting. The results are compared with other distance measurements to the Large Magellanic Cloud and M31.




3.

Radial velocities of the Milky Way clusters are used to derive the kinematics of various subsamples of the clusters (the mean rotation speed about the Galactic center, and the line-of-sight velocity dispersion). The inner metal-rich clusters behave kinematically and spatially like a flattened rotating bulge population, while the outer metal-rich clusters resemble a thick-disk population more closely. The metal-poor clusters have a significant prograde rotation (80 to 100 km s−1) in the inner halo and bulge, declining smoothly to near-zero for R ≳ R 0. No identifiable subgroups are found with significant retrograde motion.




4.

The radial velocities of the globular clusters are used along with the spherically symmetric collisionless Boltzmann equation to derive the mass profile of the Milky Way halo. The total mass of the Galaxy is near ≃ 8 × 1011 M⊙ for r ≲ 100 kpc. Extensions to still larger radii with the same formalism are extremely uncertain because of the small numbers of outermost satellites, and the possible correlations of their motions in orbital families.




5.

The luminosity functions (GCLF) of the Milky Way and M31 globular clusters are defined and analyzed. We search for possible trends with cluster metallicity or radius, and investigate different analytic fitting functions such as the Gaussian and power-law forms.




6.

The global properties of GCSs in other galaxies are reviewed. Measureable distributions include the total cluster population (quantified as the specific frequency S N), the metallicity distribution function (MDF), the luminosity and space distributions, and the radial velocity distribution.




7.

The GCLF is evaluated as a standard candle for distance determination. For giant E galaxies, the GCLF turnover has a mean luminosity of M v = −7.33 on a distance scale where Virgo has a distance modulus of 31.0 and Fornax is at 31.3, with galaxy-to-galaxy scatter σ(M v) = 0.15 mag. Applying this calibration to more remote galaxies yields a Hubble constant H 0 = (74 ± 9) km s−1 Mpc−1.




8.

The observational constraints on globular cluster formation models are summarized. The appropriate host environments for the formation of ∼ 105 to 106 M⊙ clusters are suggested to be kiloparsec-sized gas clouds (Searle/Zinn fragments or supergiant molecular clouds) of 108 to 109 M⊙. A model for the growth of proto-cluster clouds by collisional agglomeration is presented, and matched with observed mass distribution functions. The issue of globular cluster formation efficiency in different galaxies is discussed (the “specific frequency problem”).




9.

Other influences on galaxy formation are discussed, including mergers, accretions, and starbursts. Mergers of disk galaxies almost certainly produce elliptical galaxies of low S n, while the high-S N ellipticals are more likely to have been produced through in situ formation. Starburst dwarfs and large active galaxies in which current globular cluster formation is taking place are compared with the key elements of the formation model.




10.

(Appendix) Some basic principles of photometric methods are gathered together and summarized: the fundamental signal-to-noise formula, objective star finding, aperture photometry, PSF fitting, artificial-star testing, detection completeness, and photometric uncertainty. Lastly, we raise the essential issues in photometry of nonstellar objects, including image moment analysis, total magnitudes, and object classification techniques.

Globular Cluster Systems

Nearly simultaneous VLBA observations of 3C 84, the radio source associated with NGC 1275, have been made at multiple frequencies to study the free-free absorption of the northern, or counterjet, feature found by Walker, Romney, & Benson and by Vermeulen, Readhead, & Backer. Our observations confirm that the spectra are consistent with free-free absorption and eliminate the possibility that the earlier result was an effect of variability. The northern feature is well resolved spatially, so images have been made showing the distribution of the absorption over a region of about 1.5 pc on a side, beginning about 1.5 pc from the presumed location of the central object. That distribution is dominated by a strong decrease with radial distance. The magnitude of the absorption near 2.5 pc projected distance from the central object is consistent with a 104 K gas with an emission measure of about 5 × 108 pc cm-6. The geometry is consistent with absorption by ionized gas associated with an accretion disk. The data provide firm constraints for models of the outer regions of accretion disks and, perhaps, associated winds.

VLBA Absorption Imaging of Ionized Gas Associated with the Accretion Disk in NGC 1275

CO radio emission has been discovered in both the J=1-0 and J=2-1 rotational lines from the elliptical galaxy NGC 1275. The CO, which may condense from the cooling flow by means of which mass is thought to be accumulating, exhibits such a small velocity dispersion that it may collapse into stars before it virializes in the gravitational potential of this galaxy. If the star formation rate is as high as presently calculated, the initial mass function will be weighted toward the production of low-mass stars.

A. Castets

Papers

Discovery of CO emission from NGC 1275

Discovery of CO Emission from NGC1275