316 research outputs found
Multiple merging in the Abell cluster 1367
We present a dynamical analysis of the central ~1.3 square degrees of the
cluster of galaxies Abell 1367, based on 273 redshift measurements (of which
119 are news). From the analysis of the 146 confirmed cluster members we derive
a significantly non-Gaussian velocity distribution, with a mean location C_{BI}
= 6484+/-81 km/s and a scale S_{BI} = 891+/-58 km/s. The cluster appears
elongated from the North-West to the South-East with two main density peaks
associated with two substructures. The North-West subcluster is probably in the
early phase of merging into the South-East substructure (~ 0.2 Gyr before core
crossing). A dynamical study of the two subclouds points out the existence of a
group of star-forming galaxies infalling into the core of the South-East
subcloud and suggests that two other groups are infalling into the NW and SE
subclusters respectively. These three subgroups contain a higher fraction of
star-forming galaxies than the cluster core, as expected during merging events.
Abell 1367 appears as a young cluster currently forming at the intersection of
two filaments.Comment: 15 pages, 13 figures, 7 tables. Accepted for publication on A&A. High
resolution figures at http://goldmine.mib.infn.it/papers/a1367.htm
The X-ray luminosity function of galaxies in the Coma cluster
The XMM-Newton survey of the Coma cluster of galaxies covers an area of 1.86
square degrees with a mosaic of 16 pointings and has a total useful integration
time of 400 ksec. Detected X-ray sources with extent less than 10" were
correlated with cataloged galaxies in the Coma cluster region. The redshift
information, which is abundant in this region of the sky, allowed us to
separate cluster members from background and foreground galaxies. For the
background sources, we recover a typical LogN-LogS in the flux range 1.e-15 -
1.e-13 ergs/s/cm^2 in the 0.5-2.0 keV band. The X-ray emission from the cluster
galaxies exhibits X-ray colors typical of thermal emission. The luminosities of
Coma galaxies lie in the 1.e39-1.e41 ergs/s interval in the 0.5-2.0 keV band.
The luminosity function of Coma galaxies reveals that their X-ray activity is
suppressed with respect to the field by a factor of 5.6, indicating a lower
level of X-ray emission for a given stellar mass.Comment: 16 pages, 2004 A&A in pres
Effect of strontium and cooling rate upon eutectic temperatures of A319 aluminum alloy
DTA analysis was used to investigate the solidification reactions of alloy A319 with either 12 or 136 ppm of Sr added. Strontium does not affect primary solidification of (Al) dendrites but modifies the kinetics of the (Al)–Si eutectic. The effects of Sr level and of cooling rate on the characteristic temperatures for the (Al)–Si and other eutectic reactions are described
Optical spectroscopy and the UV luminosity function of galaxies in the Abell 1367, Coma and Virgo clusters
Optical spectroscopy of 93 galaxies, 60 projected in the direction of Abell
1367, 21 onto the Coma cluster and 12 on Virgo, is reported. The targets were
selected either because they were detected in previous H\alpha, UV or r'
surveys. The present observations bring to 100% the redshift completeness of
H\alpha selected galaxies in the Coma region and to 75% in Abell 1367. All
observed galaxies except one show H\alpha emission and belong to the clusters.
This confirms previous determinations of the H\alpha luminosity function of the
two clusters that were based on the assumption that all H\alpha detected
galaxies were cluster members. Using the newly obtained data we re-determine
the UV luminosity function of Coma and we compute for the first time the UV
luminosity function of A1367. Their faint end slopes remain uncertain (-2.00 <
\alpha < -1.35) due to insufficient knowledge of the background counts. If 90%
of the UV selected galaxies without redshift will be found in the background
(as our survey indicates), the slope of UV luminosity function will be \alpha ~
-1.35, in agreement with the UV luminosity function of the field (Sullivan et
al. 2000) and with the H luminosity functions of the two clusters
(Iglesias-Paramo et al. 2002). We discover a point like H\alpha source in the
Virgo cluster, associated with the giant galaxy VCC873, possibly an
extragalactic HII region similar to the one recently observed in Virgo by
Gerhard et al. (2002).Comment: 8 pages, 6 figures, 2 tables. Accepted for publication on A&
The UV luminosity function of nearby clusters of galaxies
We present the UV composite luminosity function for galaxies in the Virgo,
Coma and Abell 1367 clusters. The luminosity function (LF) is well fitted by a
Schechter function with M*(UV} - 5*log h(75) = -20.75 +/- 0.40 and alpha =
-1.50 +/- 0.10 and does not differ significantly from the local UV luminosity
function of the field. This result is in agreement with recent studies carried
out in the Halpha and B-bands which find no difference between the LFs of star
forming galaxies in clusters and in the field. This indicates that, whatever
mechanisms are responsible for quenching the star formation in clusters, they
influence similarly the giant and the dwarf populations, leaving the shape of
the LF unchanged and only modifying its normalization.Comment: 5 pages, 4 figures, 2 tables.Accepted for publication on A&A. Data
avaliable at http://goldmine.mib.infn.it/papers/LF_UV.htm
Seismic structure of the southern Gulf of California from Los Cabos block to the East Pacific Rise
Multichannel reflection and coincident wide-angle seismic data collected during the 2002 Premier Experiment, Sea of Cortez, Addressing the Development of Oblique Rifting (PESCADOR) experiment provide the most detailed seismic structure to date of the southern Gulf of California. Multichannel seismic (MCS) data were recorded with a 6-km-long streamer, 480-channel, aboard the R/V Maurice Ewing, and wide-angle data was recorded by 19 instruments spaced every similar to 12 km along the transect. The MCS and wide-angle data reveal the seismic structure across the continent-ocean transition of the rifted margin. Typical continental and oceanic crust are separated by a similar to 75-km-wide zone of extended continental crust dominated by block-faulted basement. Little lateral variation in crustal thicknesses and seismic velocities is observed in the oceanic crust, suggesting a constant rate of magmatic productivity since seafloor spreading began. Oceanic crustal thickness and mean crustal velocities suggest normal mantle temperature (1300 degrees C) and passive mantle upwelling at the early stages of seafloor spreading. The crustal thickness, width of extended continental crust, and predicted temperature conditions all indicate a narrow rift mode of extension. On the basis of upper and lower crust stretching factors, an excess of lower crust was found in the extended continental crust. Total extension along transect 5W is estimated to be similar to 35 km. Following crustal extension, new oceanic crust similar to 6.4-km-thick was formed at a rate of similar to 48 mm a(-1) to accommodate plate separation
An extragalactic HII region in the Virgo cluster
We present spectroscopic observations for six emission-line objects projected
onto the Virgo cluster. These sources have been selected from narrow band
(H\alpha+[NII]) images showing faint detectable continuum emission and EW>100
Angstrom. Five of these sources result [OIII]\lambda 5007 emitters at z ~ 0.31,
while one 122603+130724 is confirmed to be an HII region belonging to the Virgo
cluster. This point-like source has a recessional velocity of ~ 200 km/s, and
is associated with the giant galaxy VCC873 (NGC 4402). It has a higher
luminosity, star formation rate and metallicity than the extragalactic HII
region recently discovered near the Virgo galaxy VCC836 by Gerhard et al.
(2002).Comment: 7 pages, 2 figures, 4 tables. Accepted for publication on A&A. High
resolution figures and FITS images available at
http://goldmine.mib.infn.it/papers/vcc873.htm
- …