198 research outputs found
Timescale of Stellar Feedback-Driven Turbulence in the ISM: A Deep Dive into UGC 4305
Understanding the interplay of stellar feedback and turbulence in the
interstellar medium (ISM) is essential to modeling the evolution of galaxies.
To determine the timescales over which stellar feedback drives turbulence in
the ISM, we performed a spatially resolved, multi-wavelength study of the
nearby star-forming dwarf galaxy UGC 4305 (aka Holmberg II). As indicators of
turbulence on local scales (400 pc), we utilized ionized gas velocity
dispersion derived from IFU H observations and atomic gas velocity
dispersion and energy surface densities derived from HI synthesis observations
with the Very Large Array. These indicators of turbulence were tested against
star formation histories over the past 560 Myr derived from Color-Magnitude
Diagrams (CMD) using Spearman's rank correlation coefficient. The strongest
correlation identified at the 400 pc scale is between measures of HI turbulence
and star formation 70-140 Myr ago. We repeated our analysis of UGC 4305's
current turbulence and past star formation activity on multiple physical scales
(560, and 800 pc) to determine if there are indications of changes in the
correlation timescale with changes to the physical scale. No notable
correlations were found at larger physical scales emphasizing the importance of
analyzing star formation driven turbulence as a local phenomenon.Comment: 17 pages, 9 figure, accepted to A
Pegasus W: An Ultra-Faint Dwarf Galaxy Outside the Halo of M31 Not Quenched by Reionization
We report the discovery of an ultrafaint dwarf (UFD) galaxy, Pegasus W,
located on the far side of the Milky Way-M31 system and outside the virial
radius of M31. The distance to the galaxy is 915 (+60/-91) kpc, measured using
the luminosity of horizontal branch (HB) stars identified in Hubble Space
Telescope optical imaging. The galaxy has a half-light radius (r_h) of 100
(+11/-13) pc, M_V = -7.20 (+0.17/-0.16) mag, and a present-day stellar mass of
6.5 (+1.1/-1.4) x 10^4 Msun. We identify sources in the color-magnitude diagram
(CMD) that may be younger than ~500 Myr suggesting late-time star formation in
the UFD galaxy, although further study is needed to confirm these are bona fide
young stars in the galaxy. Based on fitting the CMD with stellar evolution
libraries, Pegasus W shows an extended star formation history (SFH). Using the
tau_90 metric (defined as the timescale by which the galaxy formed 90% of its
stellar mass), the galaxy was quenched only 7.4 (+2.2/-2.6) Gyr ago, which is
similar to the quenching timescale of a number of UFD satellites of M31 but
significantly more recent than the UFD satellites of the Milky Way. Such
late-time quenching is inconsistent with the more rapid timescale expected by
reionization and suggests that, while not currently a satellite of M31, Pegasus
W was nonetheless slowly quenched by environmental processes.Comment: 15 pages, 10 figures, 2 table
Discovery and Characterization of Two Ultra Faint-Dwarfs Outside the Halo of the Milky Way: Leo M and Leo K
We report the discovery of two ultra-faint dwarf galaxies, Leo M and Leo K,
that lie outside the halo of the Milky Way. Using Hubble Space Telescope
imaging of the resolved stars, we create color-magnitude diagrams reaching the
old main sequence turn-off of each system and (i) fit for structural parameters
of the galaxies; (ii) measure their distances using the luminosity of the
Horizontal Branch stars; (iii) estimate integrated magnitudes and stellar
masses; and (iv) reconstruct the star formation histories. Based on their
location in the Local Group, neither galaxy is currently a satellite of the
Milky Way, although Leo K is located ~22 kpc from the low-mass galaxy Leo T and
these two systems may have had a past interaction. Leo M and Leo K have stellar
masses of 1.5+/-0.2 x 10^4 Msun and 1.0+/-0.2 x 10^4 Msun, and were quenched
10.9 (+1.8/-0.6) Gyr and 12.6 (+0.2/-5.8) Gyr ago, respectively. Given that the
galaxies are not satellites of the MW, it is unlikely that they were quenched
by environmental processing. Instead, such low masses and early quenching
timescales are consistent with the scenario that a combination of reionization
and stellar feedback shut down star formation at early cosmic times.Comment: 12 pages, 9 figures, 1 tabl
Engineering HIV envelope protein to activate germline B cell receptors of broadly neutralizing anti-CD4 binding site antibodies
Broadly neutralizing antibodies (bnAbs) against HIV are believed to be a critical component of the protective responses elicited by an effective HIV vaccine. Neutralizing antibodies against the evolutionarily conserved CD4-binding site (CD4-BS) on the HIV envelope glycoprotein (Env) are capable of inhibiting infection of diverse HIV strains, and have been isolated from HIV-infected individuals. Despite the presence of antiβCD4-BS broadly neutralizing antibody (bnAb) epitopes on recombinant Env, Env immunization has so far failed to elicit such antibodies. Here, we show that Env immunogens fail to engage the germline-reverted forms of known bnAbs that target the CD4-BS. However, we found that the elimination of a conserved glycosylation site located in Loop D and two glycosylation sites located in variable region 5 of Env allows Env-binding to, and activation of, B cells expressing the germline-reverted BCRs of two potent broadly neutralizing antibodies, VRC01 and NIH45-46. Our results offer a possible explanation as to why Env immunogens have been ineffective in stimulating the production of such bNAbs. Importantly, they provide key information as to how such immunogens can be engineered to initiate the process of antibody-affinity maturation against one of the most conserved Env regions
Training of Instrumentalists and Development of New Technologies on SOFIA
This white paper is submitted to the Astronomy and Astrophysics 2010 Decadal
Survey (Astro2010)1 Committee on the State of the Profession to emphasize the
potential of the Stratospheric Observatory for Infrared Astronomy (SOFIA) to
contribute to the training of instrumentalists and observers, and to related
technology developments. This potential goes beyond the primary mission of
SOFIA, which is to carry out unique, high priority astronomical research.
SOFIA is a Boeing 747SP aircraft with a 2.5 meter telescope. It will enable
astronomical observations anywhere, any time, and at most wavelengths between
0.3 microns and 1.6 mm not accessible from ground-based observatories. These
attributes, accruing from the mobility and flight altitude of SOFIA, guarantee
a wealth of scientific return. Its instrument teams (nine in the first
generation) and guest investigators will do suborbital astronomy in a
shirt-sleeve environment. The project will invest $10M per year in science
instrument development over a lifetime of 20 years. This, frequent flight
opportunities, and operation that enables rapid changes of science instruments
and hands-on in-flight access to the instruments, assure a unique and extensive
potential - both for training young instrumentalists and for encouraging and
deploying nascent technologies. Novel instruments covering optical, infrared,
and submillimeter bands can be developed for and tested on SOFIA by their
developers (including apprentices) for their own observations and for those of
guest observers, to validate technologies and maximize observational
effectiveness.Comment: 10 pages, no figures, White Paper for Astro 2010 Survey Committee on
State of the Professio
Teaching Matters: Essays by UMF Faculty
Essays by faculty at the University of Maine at Farmington.https://scholarworks.umf.maine.edu/publications/1086/thumbnail.jp
An AzTEC 1.1 mm survey of the GOODS-N field β II. Multiwavelength identifications and redshift distribution
We present results from a multiwavelength study of 29 sources (false detection probabilities <5 per cent) from a survey of the Great Observatories Origins Deep Survey-North (GOODS-N) field at 1.1 mm using the Astronomical Thermal Emission Camera (AzTEC). Comparing with existing 850 ΞΌm Submillimetre Common-User Bolometer Array (SCUBA) studies in the field, we examine differences in the source populations selected at the two wavelengths. The AzTEC observations uniformly cover the entire survey field to a 1Ο depth of ~1 mJy. Searching deep 1.4 GHz Very Large Array (VLA) and Spitzer 3β24 ΞΌm catalogues, we identify robust counterparts for 21 1.1 mm sources, and tentative associations for the remaining objects. The redshift distribution of AzTEC sources is inferred from available spectroscopic and photometric redshifts. We find a median redshift of z= 2.7 , somewhat higher than z= 2.0 for 850 ΞΌm selected sources in the same field, and our lowest redshift identification lies at a spectroscopic redshift z= 1.1460 . We measure the 850 ΞΌm to 1.1 mm colour of our sources and do not find evidence for '850 ΞΌm dropouts', which can be explained by the low signal-to-noise ratio of the observations. We also combine these observed colours with spectroscopic redshifts to derive the range of dust temperatures T, and dust emissivity indices Ξ² for the sample, concluding that existing estimates T ~ 30 K and Ξ² ~ 1.75 are consistent with these new data
Preexisting memory CD4+ T cells contribute to the primary response in an HIV-1 vaccine trial
Naive and memory CD4+ T cells reactive with human immunodeficiency virus type 1 (HIV-1) are detectable in unexposed, unimmunized individuals. The contribution of preexisting CD4+ T cells to a primary immune response was investigated in 20 HIV-1βseronegative volunteers vaccinated with an HIV-1 envelope (Env) plasmid DNA prime and recombinant modified vaccinia virus Ankara (MVA) boost in the HVTN 106 vaccine trial (clinicaltrials.gov NCT02296541). Prevaccination naive or memory CD4+ T cell responses directed against peptide epitopes in Env were identified in 14 individuals. After priming with DNA, 40% (8/20) of the elicited responses matched epitopes detected in the corresponding preimmunization memory repertoires, and clonotypes were shared before and after vaccination in 2 representative volunteers. In contrast, there were no shared epitope specificities between the preimmunization memory compartment and responses detected after boosting with recombinant MVA expressing a heterologous Env. Preexisting memory CD4+ T cells therefore shape the early immune response to vaccination with a previously unencountered HIV-1 antigen
The SUMO Isopeptidase Ulp2p Is Required to Prevent Recombination-Induced Chromosome Segregation Lethality following DNA Replication Stress
SUMO conjugation is a key regulator of the cellular response to DNA replication stress, acting in part to control recombination at stalled DNA replication forks. Here we examine recombination-related phenotypes in yeast mutants defective for the SUMO de-conjugating/chain-editing enzyme Ulp2p. We find that spontaneous recombination is elevated in ulp2 strains and that recombination DNA repair is essential for ulp2 survival. In contrast to other SUMO pathway mutants, however, the frequency of spontaneous chromosome rearrangements is markedly reduced in ulp2 strains, and some types of rearrangements arising through recombination can apparently not be tolerated. In investigating the basis for this, we find DNA repair foci do not disassemble in ulp2 cells during recovery from the replication fork-blocking drug methyl methanesulfonate (MMS), corresponding with an accumulation of X-shaped recombination intermediates. ulp2 cells satisfy the DNA damage checkpoint during MMS recovery and commit to chromosome segregation with similar kinetics to wild-type cells. However, sister chromatids fail to disjoin, resulting in abortive chromosome segregation and cell lethality. This chromosome segregation defect can be rescued by overproducing the anti-recombinase Srs2p, indicating that recombination plays an underlying causal role in blocking chromatid separation. Overall, our results are consistent with a role for Ulp2p in preventing the formation of DNA lesions that must be repaired through recombination. At the same time, Ulp2p is also required to either suppress or resolve recombination-induced attachments between sister chromatids. These opposing defects may synergize to greatly increase the toxicity of DNA replication stress
Recombinant HIV Envelope Proteins Fail to Engage Germline Versions of Anti-CD4bs bNAbs
Vaccine candidates for HIV-1 so far have not been able to elicit broadly neutralizing antibodies (bNAbs) although they express the epitopes recognized by bNAbs to the HIV envelope glycoprotein (Env). To understand whether and how Env immunogens interact with the predicted germline versions of known bNAbs, we screened a large panel (N:56) of recombinant Envs (from clades A, B and C) for binding to the germline predecessors of the broadly neutralizing anti-CD4 binding site antibodies b12, NIH45-46 and 3BNC60. Although the mature antibodies reacted with diverse Envs, the corresponding germline antibodies did not display Env-reactivity. Experiments conducted with engineered chimeric antibodies combining the mature and germline heavy and light chains, respectively and vice-versa, revealed that both antibody chains are important for the known cross-reactivity of these antibodies. Our results also indicate that in order for b12 to display its broad cross-reactivity, multiple somatic mutations within its VH region are required. A consequence of the failure of the germline b12 to bind recombinant soluble Env is that Env-induced B-cell activation through the germline b12 BCR does not take place. Our study provides a new explanation for the difficulties in eliciting bNAbs with recombinant soluble Env immunogens. Our study also highlights the need for intense efforts to identify rare naturally occurring or engineered Envs that may engage the germline BCR versions of bNAbs
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