135 research outputs found
The Spitzer Archival Far-InfraRed Extragalactic Survey
We present the Spitzer Archival Far-InfraRed Extragalactic Survey (SAFIRES).
This program produces refined mosaics and source lists for all far-infrared
extragalactic data taken during the more than six years of the cryogenic
operation of the Spitzer Space Telescope. The SAFIRES products consist of
far-infrared data in two wavelength bands (70 um and 160 um) across
approximately 180 square degrees of sky, with source lists containing
far-infrared fluxes for almost 40,000 extragalactic point sources. Thus,
SAFIRES provides a large, robust archival far-infrared data set suitable for
many scientific goals.Comment: 7 pages, 6 figures, published in ApJ
Recommended from our members
Golgi derived PI(4)P-containing vesicle drives late steps of mitochondrial division
Mitochondrial plasticity is a key regulator of cell fate decisions. Mitochondrial division involves Dynamin-related protein-1 (Drp1) oligomerization, which constricts membranes at endoplasmic reticulum (ER) contact sites. The mechanisms driving the final steps of mitochondrial division are still unclear. Here, we found that microdomains of phosphatidylinositol 4-phosphate (PI(4)P) on Trans-Golgi network (TGN) vesicles were recruited to mitochondria-ER contact sites and could drive mitochondrial division downstream of Drp1. The loss of the small GTPase ADP-ribosylation factor 1 (Arf1) or its effector, phosphatidylinositol 4-kinase IIIÎČ (PI(4)KIIIÎČ) in different mammalian cell lines, prevented PI(4)P generation and led to a hyperfused and branched mitochondrial network, marked with extended mitochondrial constriction sites. Thus, recruitment of TGN-PI(4)P-containing vesicles at mitochondria-ER contact sites may trigger final events leading to mitochondrial scission.This work was supported by the Canadian Institutes of Health Research Operating Grants Program (CIHR grant 68833 to H.M.M.), the Medical Research Council (MRC grants MC_UU_00015/7 and RG89175 to J.P.), the Isaac Newton Trust (grant RG89529 to J.P.), and the Wellcome Trust Institutional Strategic Support Fund (grant RG89305 to J.P.). H.M.M. is a Canada Research Chair. S.N. and L.-C.T. are recipients of Daiichi Sankyo Foundation of Life Science and Ramon Areces postdoctoral fellowships, respectively. L.T. was supported by an MRC-funded graduate student fellowship. V.P was supported by the European Unionâs Horizon 2020 research and innovation program (MITODYN-749926)
Intergalactic HII Regions Discovered in SINGG
A number of very small isolated HII regions have been discovered at projected
distances up to 30 kpc from their nearest galaxy. These HII regions appear as
tiny emission line objects in narrow band images obtained by the NOAO Survey
for Ionization in Neutral Gas Galaxies (SINGG). We present spectroscopic
confirmation of four isolated HII regions in two systems, both systems have
tidal HI features. The results are consistent with stars forming in interactive
debris due to cloud-cloud collisions. The H-alpha luminosities of the isolated
HII regions are equivalent to the ionizing flux of only a few O stars each.
They are most likely ionized by stars formed in situ, and represent atypical
star formation in the low density environment of the outer parts of galaxies. A
small but finite intergalactic star formation rate will enrich and ionize the
surrounding medium. In one system, NGC 1533, we calculate a star formation rate
of 1.5e-3 msun/yr, resulting in a metal enrichment of ~1e-3 solar for the
continuous formation of stars. Such systems may have been more common in the
past and a similar enrichment level is measured for the `metallicity floor' in
damped Lyman-alpha absorption systems.Comment: accepted for publication in the Astronomical Journal, 19 pages,
including 5 figures, some low resolution. Paper with high resolution images
can be downloaded from
http://astro.ph.unimelb.edu.au/~eryan/publications/eldots.ps.g
Cosmic Ray Electrons in Groups and Clusters of Galaxies: Primary and Secondary Populations from a Numerical Cosmological Simulation
We study the generation and distribution of high energy electrons in cosmic
environment and their observational consequences by carrying out the first
cosmological simulation that includes directly cosmic ray (CR) particles.
Starting from cosmological initial conditions we follow the evolution of
primary and secondary electrons (CRE), CR ions (CRI) and a passive magnetic
field. CRIs and primary CREs are injected and accelerated at large scale
structure shocks. Secondary CREs are continuously generated through inelastic
p-p collisions. We include spatial transport, adiabatic expansion/compression,
Coulomb collisions, bremsstrahlung, synchrotron (SE)and inverse Compton (IC)
emission. We find that, from the perspective of cosmic shock energy and
acceleration efficiency, the few detections of hard X-ray radiation excess
could be explained in the framework of IC emission of primary CREs in clusters
undergoing high accretion/merger phase. Instead, IC emission from both primary
and secondary CREs accounts at most for a small fraction of the radiation
excesses detected in the extreme-UV (except for the Coma cluster as reported by
Bowyer et al.1999). Next, we calculate the SE after normalizing the magnetic
field so that for a Coma-like cluster ^1/2~3 \muG. Our results indicate
that the SE from secondary CREs reproduces several general properties of radio
halos, including the recently found P_1.4GHz vs T relation, the morphology and
polarization of the emitting region and, to some extent, the spectral index.
Moreover, SE from primary CREs turns out sufficient to power extended regions
resembling radio relics observed at the outskirts of clusters. Again we find
striking resemblance between morphology, polarization and spectral index of our
synthetic maps and those reported in the literature.Comment: emulateapj, 27 pages, 10 figures, 5 tables; ApJ in pres
The Survey for Ionization in Neutral Gas Galaxies- II. The Star Formation Rate Density of the Local Universe
We derive observed Halpha and R band luminosity densities of an HI-selected
sample of nearby galaxies using the SINGG sample to be l_Halpha' = (9.4 +/-
1.8)e38 h_70 erg s^-1 Mpc^-3 for Halpha and l_R' = (4.4 +/- 0.7)e37 h_70 erg
s^-1 A^-1 Mpc^-3 in the R band. This R band luminosity density is approximately
70% of that found by the Sloan Digital Sky Survey. This leads to a local star
formation rate density of log(SFRD) = -1.80 +0.13/-0.07(random) +/-
0.03(systematic) + log(h_70) after applying a mean internal extinction
correction of 0.82 magnitudes. The gas cycling time of this sample is found to
be t_gas = 7.5 +1.3/-2.1 Gyr, and the volume-averaged equivalent width of the
SINGG galaxies is EW(Halpha) = 28.8 +7.2/-4.7 A (21.2 +4.2/-3.5 A without
internal dust correction). As with similar surveys, these results imply that
SFRD(z) decreases drastically from z ~ 1.5 to the present. A comparison of the
dynamical masses of the SINGG galaxies evaluated at their optical limits with
their stellar and HI masses shows significant evidence of downsizing: the most
massive galaxies have a larger fraction of their mass locked up in stars
compared with HI, while the opposite is true for less massive galaxies. We show
that the application of the Kennicutt star formation law to a galaxy having the
median orbital time at the optical limit of this sample results in a star
formation rate decay with cosmic time similar to that given by the SFRD(z)
evolution. This implies that the SFRD(z) evolution is primarily due to the
secular evolution of galaxies, rather than interactions or mergers. This is
consistent with the morphologies predominantly seen in the SINGG sample.Comment: 15 pages, 5 figures, ApJ in press. Data available at
http://sungg.pha.jhu.edu/PubData/ Corrected: Minor typos and formatting
issues fixe
The Survey for Ionization in Neutral Gas Galaxies: I. Description and Initial Results
We introduce the Survey for Ionization in Neutral Gas Galaxies (SINGG), a
census of star formation in HI-selected galaxies. The survey consists of
H-alpha and R-band imaging of a sample of 468 galaxies selected from the HI
Parkes All Sky Survey (HIPASS). The sample spans three decades in HI mass and
is free of many of the biases that affect other star forming galaxy samples. We
present the criteria for sample selection, list the entire sample, discuss our
observational techniques, and describe the data reduction and calibration
methods. This paper focuses on 93 SINGG targets whose observations have been
fully reduced and analyzed to date. The majority of these show a single
Emission Line Galaxy (ELG). We see multiple ELGs in 13 fields, with up to four
ELGs in a single field. All of the targets in this sample are detected in
H-alpha indicating that dormant (non-star forming) galaxies with M(HI) > ~3e7
M_sun are very rare. A database of the measured global properties of the ELGs
is presented. The ELG sample spans four orders of magnitude in luminosity
(H-alpha and R-band), and H-alpha surface brightness, nearly three orders of
magnitude in R surface brightness and nearly two orders of magnitude in H-alpha
equivalent width (EW). The surface brightness distribution of our sample is
broader than that of the Sloan Digital Sky Survey spectroscopic sample, the
(EW) distribution is broader than prism-selected samples, and the morphologies
found include all common types of star forming galaxies (e.g. irregular,
spiral, blue compact dwarf, starbursts, merging and colliding systems, and even
residual star formation in S0 and Sa spirals). (abridged)Comment: 28 pages, ApJS, in press. Full resolution version with all panels of
Fig. 8 available at http://sungg.pha.jhu.edu/publications.html . On line data
available at http://sungg.pha.jhu.edu/PubData/ . Author list corrected. Wrong
value for f_ap used in eq. 7 now corrected; typos corrected, non-used
references replaced, others update
Outlying HII Regions in HI-Selected Galaxies
We present results from the first systematic search for outlying HII regions,
as part of a sample of 96 emission-line point sources (referred to as ELdots -
emission-line dots) derived from the NOAO Survey for Ionization in Neutral Gas
Galaxies (SINGG). Our automated ELdot-finder searches SINGG narrow-band and
continuum images for high equivalent width point sources outside the optical
radius of the target galaxy (> 2 X r25 in the R-band). Follow-up longslit
spectroscopy and deep GALEX images (exposure time > 1000 s) distinguish
outlying HII regions from background galaxies whose strong emission lines
([OIII], Hbeta or [OII]) have been redshifted into the SINGG bandpass. We find
that these deep GALEX images can serve as a substitute for spectroscopic
follow-up because outlying HII regions separate cleanly from background
galaxies in color-color space. We identify seven SINGG systems with outlying
massive star formation that span a large range in Halpha luminosities
corresponding to a few O stars in the most nearby cases, and unresolved dwarf
satellite companion galaxies in the most distant cases. Six of these seven
systems feature galaxies with nearby companions or interacting galaxies.
Furthermore, our results indicate that some outlying HII regions are linked to
the extended-UV disks discovered by GALEX, representing emission from the most
massive O stars among a more abundant population of lower mass (or older) star
clusters. The overall frequency of outlying HII regions in this sample of
gas-rich galaxies is 8 - 11% when we correct for background emission-line
galaxy contamination (~75% of ELdots).Comment: 20 pages, 14 Figures, Accepted by A
Three-body correlations in the Nagaoka state on the square lattice
A three-body scattering theory previously proposed by one of the present
authors is developed to be applied to the saturated ferromagnetic state in the
two-dimensional Hubbard model. The single-particle Green's function is
calculated by taking account of the multiple scattering between two electrons
and one hole. Several limiting cases are discussed and the relation to the
variational principle is examined. The importance of the three-body correlation
is demonstrated in comparison with the results of the ladder approximation. A
possible phase boundary for the Nagaoka ground state is presented for the
square lattice, which improves the previous variational results.Comment: 13 pages, 8 Postscript figures, submitted to Phys.Rev.
Far-infrared Properties of Type 1 Quasars
We use the Spitzer Space Telescope Enhanced Imaging Products and the Spitzer Archival Far-InfraRed Extragalactic Survey to study the spectral energy distributions (SEDs) of spectroscopically confirmed type 1 quasars selected from the Sloan Digital Sky Survey (SDSS). By combining the Spitzer and SDSS data with the Two Micron All Sky Survey, we are able to construct a statistically robust rest-frame 0.1-100 ÎŒm type 1 quasar template. We find that the quasar population is well-described by a single power-law SED at wavelengths less than 20 ÎŒm, in good agreement with previous work. However, at longer wavelengths, we find a significant excess in infrared luminosity above an extrapolated power-law, along with significant object-to-object dispersion in the SED. The mean excess reaches a maximum of 0.8 dex at rest-frame wavelengths near 100 ÎŒm
The JCMT Nearby Galaxies Legacy Survey VII: H\alpha{} imaging and massive star formation properties
We present H\alpha{} fluxes, star formation rates (SFRs) and equivalent
widths (EWs) for a sample of 156 nearby galaxies observed in the 12CO J=3-2
line as part of the James Clerk Maxwell Telescope Nearby Galaxies Legacy
Survey. These are derived from images and values in the literature and from new
H\alpha{} images for 72 galaxies which we publish here. We describe the sample,
observations and procedures to extract the H\alpha{} fluxes and related
quantities. We discuss the SFR properties of our sample and confirm the
well-known correlation with galaxy luminosity, albeit with high dispersion. Our
SFRs range from 0.1 to 11 Msun yr-1 with a median SFR value for the complete
sample of 0.2 Msun yr-1. This median values is somewhat lower than similar
published measurements, which we attribute, in part, to our sample being
HI-selected and, thus, not biased towards high SFRs as has frequently been the
case in previous studies. Additionally, we calculate internal absorptions for
the H\alpha{} line, A(H\alpha{}), which are lower than many of those used in
previous studies. Our derived EWs, which range from 1 to 880\AA{} with a median
value of 27\AA{}, show little dependence with luminosity but rise by a factor
of five from early- to late-type galaxies. This paper is the first in a series
aimed at comparing SFRs obtained from H\alpha{} imaging of galaxies with
information derived from other tracers of star formation and atomic and
molecular gas.Comment: Accepted for publication in MNRAS. 47 pages, 18 figure
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