20 research outputs found
FLASH redshift survey - I. Observations and Catalogue
The FLAIR Shapley-Hydra (FLASH) redshift survey catalogue consists of 4613
galaxies brighter than \bJ = 16.7 (corrected for Galactic extinction) over a
605 sq. degree region of sky in the general direction of the Local Group
motion. The survey region is an approximately 60\degr \times 10\degr strip
spanning the sky from the Shapley Supercluster to the Hydra cluster, and
contains 3141 galaxies with measured redshifts. Designed to explore the effect
of the galaxy concentrations in this direction (in particular the Supergalactic
plane and the Shapley Supercluster) upon the Local Group motion, the 68%
completeness allows us to sample the large-scale structure better than similar
sparsely-sampled surveys. The survey region does not overlap with the areas
covered by ongoing wide-angle (Sloan or 2dF) complete redshift surveys. In this
paper, the first in a series, we describe the observation and data reduction
procedures, the analysis for the redshift errors and survey completeness, and
present the survey data.Comment: 12 pages, 12 figures, mn.sty, submitted to MNRA
Suppressed radio emission in supercluster galaxies: enhanced ram pressure in merging clusters?
The environmental influence on the 1.4 GHz continuum radio emission of
galaxies is analyzed in a 600 deg2 region of the local Universe containing the
Shapley Supercluster (SSC). Galaxies in the FLASH and 6dFGS redshift surveys
are cross-identified with NVSS radio sources, selected in a subsample doubly
complete in volume and luminosity. Environmental effects are studied through a
smoothed density field (normalized with random catalogs with the same survey
edges and redshift selection function) and the distance to the nearest cluster
(R/r200, where r200 is the virial radius, whose relation to the aperture
velocity dispersion is quantified). The fraction of high radio loudness
(R_K=L_radio/L_K) galaxies in the 10 Mpc Abell 3558 cluster complex at the core
of the SSC (SSC-CR) is half as large than elsewhere. In the SSC-CR, R_K is
anti-correlated with the density of the large-scale environment and correlated
with R/r200: central brightest cluster galaxies (BCGs) in the SSC-CR are 10x
less radio-loud than BCGs elsewhere, with signs of suppressed radio loudness in
the SSC-CR also present beyond the BCGs, out to at least 0.3 r200. This
correlation is nearly as strong as the tight correlation of L_K with R/r200
(K-luminosity segregation), inside the SSC-CR. The suppression of radio
loudness in SSC-CR BCGs can be attributed to cluster-cluster mergers that
destroy the cool core and thus the supply of gas to the central AGN. We
analytically demonstrate that the low radio loudness of non-BCG galaxies within
SSC-CR clusters cannot be explained by direct major galaxy mergers or rapid
galaxy flyby collisions, but by the loss of gas supply through the enhanced ram
pressure felt when these galaxies cross the shock front between the 2 merging
clusters and are later subjected to the stronger wind from the 2nd cluster.Comment: Version consolidated with Erratum A&A 499, 4
Near-Infrared and Optical Luminosity Functions from the 6dF Galaxy Survey
Luminosity functions and their integrated luminosity densities are presented
for the 6dF Galaxy Survey (6dFGS). This ongoing survey ultimately aims to
measure around 150,000 redshifts and 15,000 peculiar velocities over almost the
entire southern sky at |b|>10 deg. The main target samples are taken from the
2MASS Extended Source Catalog and the SuperCOSMOS Sky Survey catalogue, and
comprise 138,226 galaxies complete to (K, H, J, rF, bJ) = (12.75, 13.00, 13.75,
15.60, 16.75). These samples are comparable in size to the optically-selected
Sloan Digital Sky Survey and 2dF Galaxy Redshift Survey samples, and improve on
recent near-infrared-selected redshift surveys by more than an order of
magnitude in both number and sky coverage. The partial samples used in this
paper contain a little over half of the total sample in each band and are ~90
percent complete.
Luminosity distributions are derived using the 1/Vmax, STY and SWML
estimators, and probe 1 to 2 absolute magnitudes fainter in the near-infrared
than previous surveys. The effects of magnitude errors, redshift incompleteness
and peculiar velocities have been taken into account and corrected throughout.
Generally, the 6dFGS luminosity functions are in excellent agreement with those
of similarly-sized surveys. Our data are of sufficient quality to demonstrate
that a Schechter function is not an ideal fit to the true luminosity
distribution, due to its inability to simultaneously match the faint end slope
and rapid bright end decline. Integrated luminosity densities from the 6dFGS
are consistent with an old stellar population and moderately declining star
formation rate.Comment: 20 pages, 15 figures. MNRAS published. Replaces earlier version
carrying a typo in Table 6. High resolution versions of the figures can be
obtained from http://www.aao.gov.au/local/www/6df/Publication
Barred CO emission in HE1029-1831
We present CO(1-0) and CO(2-1) line emission maps of the barred spiral active
galaxy HE1029-1831 (z=0.0403) obtained with the IRAM Plateau de Bure
Interferometer (PdBI) and in part by the Berkeley-Illinois-Maryland Association
(BIMA) observatory. The CO emission is well associated with the optical bar and
extended along it. The FWHM of the CO emission is estimated to be ~(6+-2)kpc.
The CO emission shows a strong velocity gradient along the minor axis of the
bar (PA=90degree). The molecular gas mass is estimated to be ~1.2x10^(10)Msun
which indicates a very gas rich host galaxy. Most of the molecular gas appears
to be subthermally excited and cold but we also find weak evidence for a warmer
and/or denser gas component at the southern part of the bar emission, about
\~4kpc from the galactic nucleus.Comment: accepted for publication in A&A; 6 pages and 7 figure
HI study of extremely metal-deficient dwarf galaxies. I. The Nancay Radio Telescope observations of twenty-two objects
The goal of this study is to measure parameters of the integrated HI emission
for twenty-two dwarf galaxies with oxygen abundance 12+log(O/H) in the range of
7.42 to 7.65, which are representatives of the eXtremely Metal-Deficient (XMD)
galaxy group. Some of them are expected to be similar to the well-known
candidates for local young galaxies, IZw18 and SBS 0335-052 that have most of
their baryon mass in the form of neutral gas. Therefore, the HI 21-cm line
observations are crucial to understanding their group and individual
properties. The Nancay Radio Telescope (NRT) with the upgraded focal receiver
was used for observations of the 21-cm HI-line. This permitted the detection of
the faintest sources with rms of ~1 mJy per 10.5 km/s resolution element. For
eighteen detected galaxies we present the parameters of their integrated HI
line emission and describe the data on individual objects in more detail. For
four undetected XMD galaxies, we give upper limits on their M$(HI). For 70% of
the twenty studied non low surface brightness XMD galaxies, we find evidence
(both from HI and optical data) for their interaction with neighboring objects.
In the brief discussion of the group HI properties of the observed subsample
(the total O/H range is of 0.23 dex, or a factor of 1.7), we underline the
broad distributions of the HI mass (range is of 2 orders of magnitude), of the
ratio M(HI)/L_B (of 1 order of magnitude), and of the blue luminosity (range is
of 2 orders of magnitude). We also obtained HI parameters of six galaxies that
do not belong to the XMD sample. These data increase the number of XMD galaxies
with known integrated HI parameters (or upper limits) by a factor of two. This
allows us to address statistical properties of this group, which will be
presented in a forthcoming paper. (Abridged).Comment: 11 pages, including 2 tables and 2 postscript figures. Accepted to
Astronomy and Astrophysic
The intriguing HI gas in NGC 5253: an infall of a diffuse, low-metallicity HI cloud?
(Abridged) We present new, deep HI line and 20-cm radio continuum data of the
very puzzling blue compact dwarf galaxy NGC 5253, obtained with the ATCA as
part of the `Local Volume HI Survey' (LVHIS). Our low-resolution HI maps show
the disturbed HI morphology that NGC 5253 possesses, including tails, plumes
and detached HI clouds. The high-resolution map reveals an HI plume at the SE
and an HI structure at the NW that surrounds an Ha shell. We confirm that the
kinematics of the neutral gas are highly perturbed and do not follow a rotation
pattern. We discuss the outflow and infall scenarios to explain such disturbed
kinematics, analyze the environment in which it resides, and compare it
properties with those observed in similar star-forming dwarf galaxies. The
radio-continuum emission of NGC 5253 is resolved and associated with the
intense star-forming region at the center of the galaxy. We complete the
analysis using multiwavelength data extracted from the literature. We estimate
the SFR using this multiwavelength approach. NGC 5253 does not satisfy the
Schmidt-Kennicutt law of star-formation, has a very low HI mass-to-light ratio
when comparing with its stellar mass, and seems to be slightly metal-deficient
in comparison with starbursts of similar baryonic mass. Taking into account all
available multiwavelength data, we conclude that NGC 5253 is probably
experiencing the infall of a diffuse, low-metallicity HI cloud along the minor
axis of the galaxy, which is comprising the ISM and triggering the powerful
starburst. The tidally disturbed material observed at the east and north of the
galaxy is a consequence of this interaction, which probably started more than
100 Myr ago. The origin of this HI cloud may be related with a strong
interaction between NGC 5253 and the late-type spiral galaxy M 83 in the past.Comment: 19 pages, 12 figures, accepted for publication in MNRA
ACCESS II: A Complete Census of Star Formation in the Shapley Supercluster - UV and IR Luminosity Functions
We present panoramic Spitzer/MIPS mid- and far-infrared and GALEX ultraviolet
imaging of the the most massive and dynamically active system in the local
Universe, the Shapley supercluster at z=0.048, covering the 5 clusters which
make up the supercluster core. We combine these data with existing
spectroscopic data from 814 confirmed supercluster members to produce the first
study of a local rich cluster including both ultraviolet and infrared
luminosity functions (LFs). This joint analysis allows us to produce a complete
census of star-formation (both obscured and unobscured), extending down to
SFRs~0.02-0.05Msun/yr, and quantify the level of obscuration of star formation
among cluster galaxies, providing a local benchmark for comparison to ongoing
and future studies of cluster galaxies at higher redshifts with Spitzer and
Herschel. The GALEX NUV and FUV LFs obtained have steeper faint-end slopes than
the local field population, due largely to the contribution of massive,
quiescent galaxies at M_FUV>-16. The 24um and 70um galaxy LFs for the Shapley
supercluster instead have shapes fully consistent with those obtained for the
Coma cluster and for the local field galaxy population. This apparent lack of
environmental dependence for the shape of the FIR luminosity function suggests
that the bulk of the star-forming galaxies that make up the observed cluster
infrared LF have been recently accreted from the field and have yet to have
their star formation activity significantly affected by the cluster
environment. We estimate a global SFR of 327 Msun/yr over the whole
supercluster core, of which just ~20% is visible directly in the UV continuum
and ~80% is reprocessed by dust and emitted in the infrared. The level of
obscuration (L_IR/L_FUV) in star-forming galaxies is seen to increase linearly
with L_K over two orders of magnitude in stellar mass.Comment: 19 pages, 17 figures. Accepted for publication in MNRA
ACCESS III: The Nature of Star Formation in the Shapley Supercluster
We present a joint analysis of panoramic Spitzer/MIPS mid-infrared and GALEX
ultraviolet imaging of the Shapley supercluster at z=0.048. Combining this with
spectra of 814 supercluster members and 1.4GHz radio continuum maps, this
represents the largest complete census of star-formation (both obscured and
unobscured) in local cluster galaxies to date, reaching SFRs~0.02Msun/yr. We
take advantage of this comprehensive panchromatic dataset to perform a detailed
analysis of the nature of star formation in cluster galaxies, using several
quite independent diagnostics of the quantity and intensity of star formation
to develop a coherent view of the types of star formation within cluster
galaxies. We observe a robust bimodality in the infrared (f_24/f_K) galaxy
colours, which we are able to identify as another manifestation of the broad
split into star-forming spiral and passive elliptical galaxy populations seen
in UV-optical surveys. This diagnostic also allows the identification of
galaxies in the process of having their star formation quenched as the infrared
analogue to the UV "green valley" population. The bulk of supercluster galaxies
on the star-forming sequence have specific-SFRs consistent with local field
specific-SFR-M* relations, and form a tight FIR-radio correlation confirming
that their FIR emission is due to star formation. We show that 85% of the
global SFR is quiescent star formation within spiral disks, as manifest by the
observed sequence in the IRX-beta relation being significantly offset from the
starburst relation of Kong et al. (2004), while their FIR-radio colours
indicate dust heated by low-intensity star formation. Just 15% of the global
SFR is due to nuclear starbursts. The vast majority of star formation seen in
cluster galaxies comes from normal infalling spirals who have yet to be
affected by the cluster environment.Comment: 17 pages, 9 figures. Accepted for publication in MNRA
Optical multiband surface photometry of a sample of Seyfert galaxies. I. Large-scale morphology and local environment analysis of matched Seyfert and inactive galaxy samples
Parallel analysis of the large-scale morphology and local environment of
matched active and control galaxy samples plays an important role in studies of
the fueling of active galactic nuclei. We carry out a detailed morphological
characterization of a sample of 35 Seyfert galaxies and a matched sample of
inactive galaxies in order to compare the evidence of non-axisymmetric
perturbation of the potential and, in the second part of this paper, to be able
to perform a multicomponent photometric decomposition of the Seyfert galaxies.
We constructed contour maps, BVRcIc profiles of the surface brightness,
ellipticity, and position angle, as well as colour index profiles. We further
used colour index images, residual images, and structure maps, which helped
clarify the morphology of the galaxies. We studied the presence of close
companions using literature data. By straightening out the morphological status
of some of the objects, we derived an improved morphological classification and
built a solid basis for a further multicomponent decomposition of the Seyfert
sample. We report hitherto undetected (to our knowledge) structural components
in some Seyfert galaxies - a bar (Ark 479), an oval/lens (Mrk 595), rings (Ark
120, Mrk 376), a nuclear bar and ring (Mrk 352), and nuclear dust lanes (Mrk
590). We compared the large-scale morphology and local environment of the
Seyfert sample to those of the control one and found that (1) the two samples
show similar incidences of bars, rings, asymmetries, and close companions; (2)
the Seyfert bars are generally weaker than the bars of the control galaxies;
(3) the bulk of the two samples shows morphological evidence of
non-axisymmetric perturbations of the potential or close companions; (4) the
fueling of Seyfert nuclei is not directly related to the large-scale morphology
and local environment of their host galaxies.Comment: Accepted for publication in A&