1,607 research outputs found
MMTF: The Maryland-Magellan Tunable Filter
This paper describes the Maryland-Magellan Tunable Filter (MMTF) on the
Magellan-Baade 6.5-meter telescope. MMTF is based on a 150-mm clear aperture
Fabry-Perot (FP) etalon that operates in low orders and provides transmission
bandpass and central wavelength adjustable from ~5 to ~15 A and from ~5000 to
over ~9200 A, respectively. It is installed in the Inamori Magellan Areal
Camera and Spectrograph (IMACS) and delivers an image quality of ~0.5" over a
field of view of 27' in diameter (monochromatic over ~10'). This versatile and
easy-to-operate instrument has been used over the past three years for a wide
variety of projects. This paper first reviews the basic principles of FP
tunable filters, then provides a detailed description of the hardware and
software associated with MMTF and the techniques developed to observe with this
instrument and reduce the data. The main lessons learned in the course of the
commissioning and implementation of MMTF are highlighted next, before
concluding with a brief outlook on the future of MMTF and of similar facilities
which are soon coming on line.Comment: 38 pages, 12 figures, 3 tables, now accepted for publication to the
Astronomical Journa
Kinematics of diffuse ionized gas in the disk halo interface of NGC 891 from Fabry-P\'erot observations
The properties of the gas in halos of galaxies constrain global models of the
interstellar medium. Kinematical information is of particular interest since it
is a clue to the origin of the gas. Here we report observations of the
kinematics of the thick layer of the diffuse ionized gas in NGC 891 in order to
determine the rotation curve of the halo gas. We have obtained a Fabry-P\'erot
data cube in Halpha to measure the kinematics of the halo gas with angular
resolution much higher than obtained from HI 21 cm observations. The data cube
was obtained with the TAURUS II spectrograph at the WHT on La Palma. The
velocity information of the diffuse ionized gas extracted from the data cube is
compared to model distributions to constrain the distribution of the gas and in
particular the halo rotation curve. The best fit model has a central
attenuation tau_H-alpha=6, a dust scale length of 8.1 kpc, an ionized gas scale
length of 5.0 kpc. Above the plane the rotation curve lags with a vertical
gradient of -18.8 km/s/kpc. We find that the scale length of the H-alpha must
be between 2.5 and 6.5 kpc. Furthermore we find evidence that the rotation
curve above the plane rises less steeply than in the plane. This is all in
agreement with the velocities measured in the HI.Comment: A&A, in press. 13 pages, 19 figure
Galaxy And Mass Assembly (GAMA)
The GAMA survey aims to deliver 250,000 optical spectra (3--7Ang resolution)
over 250 sq. degrees to spectroscopic limits of r_{AB} <19.8 and K_{AB}<17.0
mag. Complementary imaging will be provided by GALEX, VST, UKIRT, VISTA,
HERSCHEL and ASKAP to comparable flux levels leading to a definitive
multi-wavelength galaxy database. The data will be used to study all aspects of
cosmic structures on 1kpc to 1Mpc scales spanning all environments and out to a
redshift limit of z ~ 0.4. Key science drivers include the measurement of: the
halo mass function via group velocity dispersions; the stellar, HI, and
baryonic mass functions; galaxy component mass-size relations; the recent
merger and star-formation rates by mass, types and environment. Detailed
modeling of the spectra, broad SEDs, and spatial distributions should provide
individual star formation histories, ages, bulge-disc decompositions and
stellar bulge, stellar disc, dust disc, neutral HI gas and total dynamical
masses for a significant subset of the sample (~100k) spanning both the giant
and dwarf galaxy populations. The survey commenced March 2008 with 50k spectra
obtained in 21 clear nights using the Anglo Australian Observatory's new
multi-fibre-fed bench-mounted dual-beam spectroscopic system (AAOmega).Comment: Invited talk at IAU 254 (The Galaxy Disk in Cosmological Context,
Copenhagen), 6 pages, 5 figures, high quality PDF version available at
http://www.eso.org/~jliske/gama
The neutral gas extent of galaxies as derived from weak intervening CaII absorbers
(Abridged) We present a systematic study of weak intervening CaII absorbers
at low redshift (z<0.5), based on the analysis of archival high resolution
(R>45,000) optical spectra of 304 quasars and active galactic nuclei observed
with VLT/UVES. Along a total redshift path of Dz~100 we detected 23 intervening
CaII absorbers in both the CaII H & K lines, with rest frame equivalent widths
W_r,3934=15-799 mA and column densities log N(CaII)=11.25-13.04. We obtain a
bias corrected number density of weak intervening CaII absorbers of
dN/dz=0.117+-0.044 at z=0.35 for absorbers with log N(CaII)>11.65. This is ~2.6
times the value obtained for damped Lyman alpha absorbers (DLAs) at low
redshift. From ionization modeling we conclude that intervening CaII absorption
with log N(CaII)>11.5 arises in optically thick neutral gas in DLAs, sub-DLAs
and Lyman limit systems (LLS) at HI column densities of log N(HI)>17.4. The
relatively large cross section of these absorbers together with the frequent
detection of CaII absorption in high velocity clouds (HVCs) in the halo of the
Milky Way suggests that a considerable fraction of the intervening CaII systems
trace dusty neutral gas structures in the halos and circumgalactic environment
of galaxies (i.e., they are HVC analogs). Considering all galaxies with
luminosities L>0.05L* we calculate that the characteristic radial extent of
(partly) neutral gas clouds with log N(HI)>17.4 around low-redshift galaxies is
R_HVC ~ 55 kpc.Comment: 20 pages, 15 figures; A&A, in press; this revision contains several
changes that improve clarity of presentation reflecting the suggestions made
by the refere
Gamma-Rays and the Far-Infrared-Radio Continuum Correlation Reveal a Powerful Galactic Centre Wind
We consider the thermal and non-thermal emission from the inner 200 pc of the
Galaxy. The radiation from this almost star-burst-like region is ultimately
driven dominantly by on-going massive star formation. We show that this
region's radio continuum (RC) emission is in relative deficit with respect to
the expectation afforded by the Far- infrared-Radio Continuum Correlation
(FRC). Likewise we show that the region's gamma-ray emission falls short of
that expected given its star formation and resultant supernova rates. These
facts are compellingly explained by positing that a powerful (400-1200 km/s)
wind is launched from the region. This wind probably plays a number of
important roles including advecting positrons into the Galactic bulge thus
explaining the observed ~kpc extension of the 511 keV positron annihilation
signal around the GC. We also show that the large-scale GC magnetic field falls
in the range ~100-300 microG and that - in the time they remain in the region -
GC cosmic rays do not penetrate into the region's densest molecular material.Comment: Version accepted for publication in MNRAS Letters. Discussion
extended and references adde
Galaxy And Mass Assembly (GAMA): the 0.013 < z < 0.1 cosmic spectral energy distribution from 0.1 m to 1 mm
We use the Galaxy And Mass Assembly survey (GAMA) I data set combined with GALEX, Sloan Digital Sky Survey (SDSS) and UKIRT Infrared Deep Sky Survey (UKIDSS) imaging to construct the low-redshift (z < 0.1) galaxy luminosity functions in FUV, NUV, ugriz and YJHK bands from within a single well-constrained volume of 3.4 × 105 (Mpc h−1)3. The derived luminosity distributions are normalized to the SDSS data release 7 (DR7) main survey to reduce the estimated cosmic variance to the 5 per cent level. The data are used to construct the cosmic spectral energy distribution (CSED) from 0.1 to 2.1 μm free from any wavelength-dependent cosmic variance for both the elliptical and non-elliptical populations. The two populations exhibit dramatically different CSEDs as expected for a predominantly old and young population, respectively. Using the Driver et al. prescription for the azimuthally averaged photon escape fraction, the non-ellipticals are corrected for the impact of dust attenuation and the combined CSED constructed. The final results show that the Universe is currently generating (1.8 ± 0.3) × 1035 h W Mpc−3 of which (1.2 ± 0.1) × 1035 h W Mpc−3 is directly released into the inter-galactic medium and (0.6 ± 0.1) × 1035 h W Mpc−3 is reprocessed and reradiated by dust in the far-IR. Using the GAMA data and our dust model we predict the mid- and far-IR emission which agrees remarkably well with available data. We therefore provide a robust description of the pre- and post-dust attenuated energy output of the nearby Universe from 0.1 μm to 0.6 mm. The largest uncertainty in this measurement lies in the mid- and far-IR bands stemming from the dust attenuation correction and its currently poorly constrained dependence on environment, stellar mass and morphology
The SAMI pilot survey: The kinematic morphology-density relation in Abell 85, Abell 168 and Abell 2399
We examine the kinematic morphology of early-type galaxies (ETGs) in three galaxy clusters Abell 85, 168 and 2399. Using data from the Sydney-AAOMulti-object Integral field spectrograph we measure spatially resolved kinematics for 79 ETGs in these clusters. We calculate λR, a proxy for the projected specific stellar angular momentum, for each galaxy and classify the 79 ETGs in our samples as fast or slow rotators. We calculate the fraction of slow rotators in the ETG populations (fSR) of the clusters to be 0.21 ± 0.08, 0.08 ± 0.08 and 0.12 ± 0.06 for Abell 85, 168 and 2399, respectively, with an overall fraction of 0.15 ± 0.04. These numbers are broadly consistent with the values found in the literature, confirming recent work asserting that the fraction of slow rotators in the ETG population is constant across many orders of magnitude in global environment. We examine the distribution of kinematic classes in each cluster as a function of environment using the projected density of galaxies: the kinematic morphology-density relation.We find that in Abell 85 fSR increases in higher density regions but in Abell 168 and 2399 this trend is not seen. We examine the differences between the individual clusters to explain this. In addition, we find slow rotators on the outskirts of two of the clusters studied, Abell 85 and 2399. These galaxies reside in intermediate to low density regions and have clearly not formed at the centre of a cluster environment. We hypothesize that they formed at the centres of groups and are falling into the clusters for the first time
GAMA: towards a physical understanding of galaxy formation
The Galaxy And Mass Assembly (GAMA) project is the latest in a tradition of
large galaxy redshift surveys, and is now underway on the 3.9m Anglo-Australian
Telescope at Siding Spring Observatory. GAMA is designed to map extragalactic
structures on scales of 1kpc - 1Mpc in complete detail to a redshift of z~0.2,
and to trace the distribution of luminous galaxies out to z~0.5. The principal
science aim is to test the standard hierarchical structure formation paradigm
of Cold Dark Matter (CDM) on scales of galaxy groups, pairs, discs, bulges and
bars. We will measure (1) the Dark Matter Halo Mass Function (as inferred from
galaxy group velocity dispersions); (2) baryonic processes, such as star
formation and galaxy formation efficiency (as derived from Galaxy Stellar Mass
Functions); and (3) the evolution of galaxy merger rates (via galaxy close
pairs and galaxy asymmetries). Additionally, GAMA will form the central part of
a new galaxy database, which aims to contain 275,000 galaxies with
multi-wavelength coverage from coordinated observations with the latest
international ground- and space-based facilities: GALEX, VST, VISTA, WISE,
HERSCHEL, GMRT and ASKAP. Together, these data will provide increased depth
(over 2 magnitudes), doubled spatial resolution (0.7"), and significantly
extended wavelength coverage (UV through Far-IR to radio) over the main SDSS
spectroscopic survey for five regions, each of around 50 deg^2. This database
will permit detailed investigations of the structural, chemical, and dynamical
properties of all galaxy types, across all environments, and over a 5 billion
year timeline.Comment: GAMA overview which appeared in the October 2009 issue of Astronomy &
Geophysics, ref: Astron.Geophys. 50 (2009) 5.1
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