21 research outputs found
Observations of cold dust in nearby elliptical galaxies
Spectral energy distribution (SED) analyses that include new millimeter to far-infrared (FIR) observations obtained with continuum instruments on the Nobeyama and James Clerk Maxwell Telescopes and the Infrared Space Observatory are presented for seven nearby (<45 Mpc) FIR-bright elliptical galaxies. These are analyzed together with archival FIR and shortwave radio data obtained from the NASA/IPAC Extragalactic Database (NED). The radio to infrared SEDs are best-fitted by power law plus graybody models of dust residing in the central galactic regions within a 2.4 kpc diameter and with temperatures between ~21 and 28 K, emissivity index simeq2, and masses from ~1.6 to 19 × 105 M☉. The emissivity index is consistent with dust constituting amorphous silicate and carbonaceous grains previously modeled for stellar-heated dust observed in the Galaxy and other nearby extragalactic sources. Using updated dust absorption coefficients for this type of dust, dust masses are estimated that are similar to those determined from earlier FIR data alone, even though the latter results implied hotter dust temperatures. Fluxes and masses that are consistent with the new FIR and submillimeter data are estimated for dust cooler than 20 K within the central galactic regions. Tighter physical constraints for such cold, diffuse dust (if it exists) with low surface brightness will need sensitive FIR to submillimeter observations with the Spitzer Space Telescope, SCUBA2, or ALMA
Submillimeter Continuum Properties of Cold Dust in the Inner Disk and Outflows of M82
Deep submillimeter (submm) continuum imaging observations of the starburst
galaxy M82 are presented at 350, 450, 750 and 850 micron wavelengths, that were
undertaken with the Submillimetre Common-User Bolometer Array (SCUBA) on the
James Clerk Maxwell Telescope in Hawaii. The presented maps include a
co-addition of submm data mined from the SCUBA Data Archive. The co-added data
produce the deepest submm continuum maps yet of M82, in which low-level 850
micron continuum has been detected out to 1.5kpc, at least 10% farther in
radius than any previously published submm detections of this galaxy. The
overall submm morphology and spatial spectral energy distribution of M82 have a
general north-south asymmetry consistent with H-alpha and X-ray winds,
supporting the association of the extended continuum with outflows of dust
grains from the disk into the halo. The new data raise interesting points about
the origin and structure of the submm emission in the inner disk of M82. In
particular, SCUBA short wavelength evidence of submm continuum peaks that are
asymmetrically distributed along the galactic disk suggests the inner-disk
emission is re-radiation from dust concentrations along a bar (or perhaps a
spiral) rather than edges of a dust torus, as is commonly assumed. Higher
resolution submm interferometery data from the Smithsonian Submillimeter Array
and later Atacama Large Millimeter Array should spatially resolve and further
constrain the reported dust emission structures in M82.Comment: Accepted by the Astronomical Journal -- 28 pages and 14 figure
MeerKLASS: MeerKAT Large Area Synoptic Survey
We discuss the ground-breaking science that will be possible with a wide area
survey, using the MeerKAT telescope, known as MeerKLASS (MeerKAT Large Area
Synoptic Survey). The current specifications of MeerKAT make it a great fit for
science applications that require large survey speeds but not necessarily high
angular resolutions. In particular, for cosmology, a large survey over for hours will potentially provide the first
ever measurements of the baryon acoustic oscillations using the 21cm intensity
mapping technique, with enough accuracy to impose constraints on the nature of
dark energy. The combination with multi-wavelength data will give unique
additional information, such as exquisite constraints on primordial
non-Gaussianity using the multi-tracer technique, as well as a better handle on
foregrounds and systematics. Such a wide survey with MeerKAT is also a great
match for HI galaxy studies, providing unrivalled statistics in the pre-SKA era
for galaxies resolved in the HI emission line beyond local structures at z >
0.01. It will also produce a large continuum galaxy sample down to a depth of
about 5\,Jy in L-band, which is quite unique over such large areas and
will allow studies of the large-scale structure of the Universe out to high
redshifts, complementing the galaxy HI survey to form a transformational
multi-wavelength approach to study galaxy dynamics and evolution. Finally, the
same survey will supply unique information for a range of other science
applications, including a large statistical investigation of galaxy clusters as
well as produce a rotation measure map across a huge swathe of the sky. The
MeerKLASS survey will be a crucial step on the road to using SKA1-MID for
cosmological applications and other commensal surveys, as described in the top
priority SKA key science projects (abridged).Comment: Larger version of the paper submitted to the Proceedings of Science,
"MeerKAT Science: On the Pathway to the SKA", Stellenbosch, 25-27 May 201
The causes of the red sequence, the blue cloud, the green valley, and the green mountain
The galaxies found in optical surveys fall in two distinct regions of a diagram of optical colour versus absolute magnitude: the red sequence and the blue cloud with the green valley in between. We show that the galaxies found in a submillimetre survey have almost the opposite distribution in this diagram, forming a `green mountain'. We show that these distinctive distributions follow naturally from a single, continuous, curved Galaxy Sequence in a diagram of specific star-formation rate versus stellar mass without there being the need for a separate star-forming galaxy Main Sequence and region of passive galaxies. The cause of the red sequence and the blue cloud is the geometric mapping between stellar mass/specific star-formation rate and absolute magnitude/colour, which distorts a continuous Galaxy Sequence in the diagram of intrinsic properties into a bimodal distribution in the diagram of observed properties. The cause of the green mountain is Malmquist bias in the submillimetre waveband, with submillimetre surveys tending to select galaxies on the curve of the Galaxy Sequence, which have the highest ratios of submillimetre-to-optical luminosity. This effect, working in reverse, causes galaxies on the curve of the Galaxy Sequence to be underrepresented in optical samples, deepening the green valley. The green valley is therefore not evidence (1) for there being two distinct populations of galaxies, (2) for galaxies in this region evolving more quickly than galaxies in the blue cloud and the red sequence, (c) for rapid quenching processes in the galaxy population
Gemini Imaging of Mid-IR Emission from the Nuclear Region of Centaurus A
We present high spatial resolution mid-IR images of the nuclear region of NGC
5128 (Centaurus A). Images were obtained at 8.8 micron, N-band (10.4 micron),
and 18.3 micron using the mid-IR imager/spectrometer T-ReCS on Gemini South.
These images show a bright unresolved core surrounded by low-level extended
emission. We place an upper limit to the size of the unresolved nucleus of 3.2
pc (0.19") at 8.8 micron and 3.5 pc (0.21") at 18.3 micron at the level of the
FWHM. The most likely source of nuclear mid-IR emission is from a dusty torus
and possibly dusty narrow line region with some contribution from synchrotron
emission associated with the jet as well as relatively minor starburst
activity. Clumpy tori models are presented which predict the mid-IR size of
this torus to be no larger than 0.05" (0.85pc). Surrounding the nucleus is
extensive low-level mid-IR emission. Previously observed by ISO and Spitzer,
this paper presents to date the highest spatial resolution mid-IR images of
this extended near nuclear structure. Much of the emission is coincident with
Pa-alpha sources seen by HST implying emission from star forming areas, however
evidence for jet induced star formation, synchrotron emission from the jet, a
nuclear bar/ring, and an extended dusty narrow emission line region is also
discussed.Comment: 22 pages, 6 figures, accepted by Ap
The causes of the red sequence, the blue cloud, the green valley, and the green mountain
The galaxies found in optical surveys fall in two distinct regions of a diagram of optical colour versus absolute magnitude: the red sequence and the blue cloud, with the green valley in between. We show that the galaxies found in a submillimetre survey have almost the opposite distribution in this diagram, forming a \u27green mountain\u27. We show that these distinctive distributions follow naturally from a single, continuous, curved Galaxy Sequence in a diagram of specific star formation rate versus stellar mass, without there being the need for a separate star-forming galaxy main sequence and region of passive galaxies. The cause of the red sequence and the blue cloud is the geometric mapping between stellar mass/specific star formation rate and absolute magnitude/colour, which distorts a continuous Galaxy Sequence in the diagram of intrinsic properties into a bimodal distribution in the diagram of observed properties. The cause of the green mountain isMalmquist bias in the submillimetre waveband, with submillimetre surveys tending to select galaxies on the curve of the Galaxy Sequence, which have the highest ratios of submillimetre-to-optical luminosity. This effect, working in reverse, causes galaxies on the curve of the Galaxy Sequence to be underrepresented in optical samples, deepening the green valley. The green valley is therefore not evidence (1) for there being two distinct populations of galaxies, (2) for galaxies in this region evolving more quickly than galaxies in the blue cloud and the red sequence, and (3) for rapid-quenching processes in the galaxy population