2,013 research outputs found
From Spitzer Galaxy Photometry to Tully-Fisher Distances
This paper involves a data release of the observational campaign: Cosmicflows
with Spitzer (CFS). Surface photometry of the 1270 galaxies constituting the
survey is presented. An additional ~ 400 galaxies from various other Spitzer
surveys are also analyzed. CFS complements the Spitzer Survey of Stellar
Structure in Galaxies, that provides photometry for an additional 2352
galaxies, by extending observations to low galactic latitudes (|b|<30 degrees).
Among these galaxies are calibrators, selected in K band, of the Tully-Fisher
relation. The addition of new calibrators demonstrate the robustness of the
previously released calibration. Our estimate of the Hubble constant using
supernova host galaxies is unchanged, H0 = 75.2 +/- 3.3 km/s/Mpc.
Distance-derived radial peculiar velocities, for the 1935 galaxies with all the
available parameters, will be incorporated into a new data release of the
Cosmicflows project. The size of the previous catalog will be increased by 20%,
including spatial regions close to the Zone of Avoidance.Comment: Accepted for publication in MNRAS, 16 pages, 14 figures, 6 table
A Call to Address Academic Difficulties Resulting from the COVID-19-Related Change in Education Delivery
As the corona virus pandemic forced school closures worldwide, online platforms have become invaluable tools for allowing instruction to continue smoothly and, hopefully, for mitigating the severity of any student learning disruptions associated with the COVID-19 forced school closures. Although distance-learning is currently necessary, it is a blunt tool that may prove to be inadequate, compared to face-to-face teaching content delivery, for meeting students’ educational needs resulting from COVID-19-forced school closures. It is very likely that the sudden shift to distance-learning has will disadvantage many students who are not experienced with or prepared for the dramatic changes that have occurred in the delivery of formal education. Here, we proffer a call to education-scholars to engage in investigations designed to provide research-informed knowledge and understanding of what pedagogical methodologies are needed for addressing learning deficiencies inherent in distance-learning instruction, and to effectuate the changes needed to provide an equitable educational experience to all students, during the uncertain times of the COVID-19 pandemic
Binary Galaxies in the Local Supercluster and Its Neighborhood
We report a catalog of 509 pairs identified among 10403 nearby galaxies with
line-of-sight velocities V_LG < 3500 km/s.We selected binary systems in
accordance with two criteria (bounding and temporal), which require the
physical pair of galaxies to have negative total energy and its components to
be located inside the zero-velocity surface. We assume that individual galaxy
masses are proportional to their total K-band luminosities, M = L_K x 6M/L. The
catalog gives the magnitudes and morphological types of galaxies and also the
projected (orbital) masses and pair isolation indices. The component
line-of-sight velocity differences and projected distances of the binary
systems considered have power-law distributions with the median values of 35
km/s and 123 kpc, respectively. The median mass-to-K-band luminosity ratio is
equal to 11 M/L, and its uncertainty is mostly due to the errors of measured
velocities. Our sample of binary systems has a typical density contrast of d
ro/ro_c ~ 500 and a median crossing time of about 3.5 Gyr. We point out the
substantial fraction of binary systems consisting of late-type dwarf galaxies,
where the luminosities of both components are lower than that of the Small
Magellanic Cloud. The median projected distance for 41 such pairs is only 30
kpc, and the median difference of their line-of-sight velocities is equal to 14
km/s which is smaller than the typical error for radial-velocity (30 km/s).
This specific population of gas-rich dwarf binary galaxies such as I Zw 18 may
be at the stage immediately before merging of its components. Such objects,
which are usually lost in flux-limited (and not distance-limited) samples
deserve a thorough study in the HI radio line with high spatial and velocity
resolution.Comment: published in Astrophysical Bulletin, 2008, Vol. 63, No. 4, pp.
299-34
Towards a Full Census of the Obscure(d) Vela Supercluster using MeerKAT
Recent spectroscopic observations of a few thousand partially obscured
galaxies in the Vela constellation revealed a massive overdensity on
supercluster scales straddling the Galactic Equator (l 272.5deg) at km/s. It remained unrecognised because it is located just beyond the
boundaries and volumes of systematic whole-sky redshift and peculiar velocity
surveys - and is obscured by the Milky Way. The structure lies close to the
apex where residual bulkflows suggest considerable mass excess. The uncovered
Vela Supercluster (VSCL) conforms of a confluence of merging walls, but its
core remains uncharted. At the thickest foreground dust column densities (|b| <
6 deg) galaxies are not visible and optical spectroscopy is not effective. This
precludes a reliable estimate of the mass of VSCL, hence its effect on the
cosmic flow field and the peculiar velocity of the Local Group. Only systematic
HI-surveys can bridge that gap. We have run simulations and will present
early-science observing scenarios with MeerKAT 32 (M32) to complete the census
of this dynamically and cosmologically relevant supercluster. M32 has been put
forward because this pilot project will also serve as precursor project for HI
MeerKAT Large Survey Projects, like Fornax and Laduma. Our calculations have
shown that a survey area of the fully obscured part of the supercluster, where
the two walls cross and the potential core of the supercluster resides, can be
achieved on reasonable time-scales (200 hrs) with M32.Comment: 10 pages, 3 figures, accepted for publication, Proceedings of
Science, workshop on "MeerKAT Science: On the Pathway to the SKA", held in
Stellenbosch 25-27 May 201
A GBT Survey of the HALOGAS Galaxies and Their Environments I: Revealing the full extent of HI around NGC891, NGC925, NGC4414 & NGC4565
We present initial results from a deep neutral hydrogen (HI) survey of the
HALOGAS galaxy sample, which includes the spiral galaxies NGC891, NGC925,
NGC4414, and NGC4565, performed with the Robert C. Byrd Green Bank Telescope
(GBT). The resulting observations cover at least four deg around these
galaxies with an average 5 detection limit of 1.210
cm over a velocity range of 20 km s and angular scale of 9.1.
In addition to detecting the same total flux as the GBT data, the spatial
distribution of the GBT and original Westerbork Synthesis Radio Telescope
(WSRT) data match well at equal spatial resolutions. The HI mass fraction below
HI column densities of 10 cm is, on average, 2\%. We discuss the
possible origins of low column density HI of nearby spiral galaxies. The
absence of a considerable amount of newly detected HI by the GBT indicates
these galaxies do not have significant extended diffuse HI structures, and
suggests future surveys planned with the SKA and its precursors must go
\textit{at least} as deep as 10 cm in column density to
significantly increase the probability of detecting HI associated with the
cosmic web and/or cold mode accretion.Comment: Accepted for publication in The Astrophysical Journal; 28 pages, 15
figure
The First Supernova Explosions: Energetics, Feedback, and Chemical Enrichment
We perform three-dimensional smoothed particle hydrodynamics simulations in a
realistic cosmological setting to investigate the expansion, feedback, and
chemical enrichment properties of a 200 M_sun pair-instability supernova in the
high-redshift universe. We find that the SN remnant propagates for a Hubble
time at z = 20 to a final mass-weighted mean shock radius of 2.5 kpc (proper),
roughly half the size of the HII region, and in this process sweeps up a total
gas mass of 2.5*10^5 M_sun. The morphology of the shock becomes highly
anisotropic once it leaves the host halo and encounters filaments and
neighboring minihalos, while the bulk of the shock propagates into the voids of
the intergalactic medium. The SN entirely disrupts the host halo and terminates
further star formation for at least 200 Myr, while in our specific case it
exerts positive mechanical feedback on neighboring minihalos by
shock-compressing their cores. In contrast, we do not observe secondary star
formation in the dense shell via gravitational fragmentation, due to the
previous photoheating by the progenitor star. We find that cooling by metal
lines is unimportant for the entire evolution of the SN remnant, while the
metal-enriched, interior bubble expands adiabatically into the cavities created
by the shock, and ultimately into the voids with a maximum extent similar to
the final mass-weighted mean shock radius. Finally, we conclude that dark
matter halos of at least M_vir > 10^8 M_sun must be assembled to recollect all
components of the swept-up gas.Comment: 16 pages, 14 figures, published in Ap
A Massive Spiral Galaxy in the Zone of Avoidance
We report the discovery of a very HI-massive disk galaxy, HIZOA J0836-43, at
a velocity of v_hel = 10689 km/s, corresponding to a distance of 148 Mpc
(assuming H_0=75 km/s/Mpc). It was found during the course of a systematic HI
survey of the southern Zone of Avoidance (|b| < 5 deg) with the multibeam
system at the 64m Parkes radio telescope. Follow-up observations with the
Australia Telescope Compact Array (ATCA) reveal an extended HI disk. We derive
an HI mass of 7.5 x 10^10 Msun. Using the HI radius, we estimate a total
dynamical mass of 1.4 x 10^12 Msun, similar to the most massive known disk
galaxies such as Malin 1. HIZOA J0836-43 lies deep in the Zone of Avoidance (l,
b = 262.48 deg, -1.64 deg) where the optical extinction is very high, A_B =
9.8. However, in the near-infrared wavebands, where the extinction is
considerably lower, HIZOA J0836-43 is clearly detected by both DENIS and 2MASS.
Deep AAT near-infrared (Ks and H-band) images show that HIZOA J0836-43 is an
inclined disk galaxy with a prominent bulge (scale length 2.5 arcsec or 1.7
kpc), and an extended disk (scale length 7 arcsec or 4.7 kpc) which can be
traced along the major axis out to a radius of 20 arcsec or 13.4 kpc (at 20
mag/arcsec^2 in Ks). The HI disk is much more extended, having a radius of 66
kpc at 1 Msun/pc^2. Detections in the radio continuum at 1.4 GHz and at 60
micron (IRAS) are consistent with HIZOA J0836-43 forming stars at a rate of ~35
Msun/yr. We compare the properties of HIZOA J0836-43 with those of the most
HI-massive galaxies currently known, UGC 4288, UGC 1752 and Malin 1, all of
which are classified as giant low surface brightness galaxies.Comment: Accepted for publication in MNRAS, 17 pages, 11 figures, 7 tables,
version with high-resolution figures available at:
http://frodo.as.arizona.edu/~jdonley/massive
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