37 research outputs found
CYGNSS: Lessons We are Learning from a Class D Mission
CYGNSS: Lessons Learned from NASA Class D Mission and how they selected their parts for the program to include balance between cost, risk, schedule and technology available as well as balancing cost restraints with mission risk profile
Discovery of a Metal-Line Absorber Associated with a Local Dwarf Starburst Galaxy
We present optical and near-infrared images, H I 21 cm emission maps, optical
spectroscopy, and Hubble Space Telescope/Space Telescope Imaging Spectrograph
ultraviolet spectroscopy of the QSO/galaxy pair SBS 1122+594/IC 691. The QSO
sight line lies at a position angle of 27 degrees from the minor axis of the
nearby dwarf starburst galaxy IC 691 (cz_gal = 1204+-3 km/s, L_B ~ 0.09 L*,
current star formation rate = 0.08-0.24 solar masses per year) and 33 kpc (6.6
arcmin) from its nucleus. We find that IC 691 has an H I mass of M_HI =
(3.6+-0.1) x 10^8 solar masses and a dynamical mass of M_dyn = (3.1+-0.5) x
10^10 solar masses. The UV spectrum of SBS 1122+594 shows a metal-line
(Ly-alpha + C IV) absorber near the redshift of IC 691 at cz_abs = 1110+-30
km/s. Since IC 691 is a dwarf starburst and the SBS 1122+594 sight line lies in
the expected location for an outflowing wind, we propose that the best model
for producing this metal-line absorber is a starburst wind from IC 691. We
place consistent metallicity limits on IC 691 ([Z/Zsun] ~ -0.7) and the
metal-line absorber ([Z/Zsun] < -0.3). We also find that the galaxy's escape
velocity at the absorber location is v_esc = 80+-10 km/s and derive a wind
velocity of v_w = 160+-50 km/s. Thus, the evidence suggests that IC 691
produces an unbound starburst wind that escapes from its gravitational
potential to transport metals and energy to the surrounding intergalactic
medium.Comment: 31 pages, 8 figures; AJ in press; a version with high resolution
figures can be downloaded from
http://casa.colorado.edu/~keeney/research/papers/IC691.pd
A Budget and Accounting of Metals at z~0: Results from the COS-Halos Survey
We present a budget and accounting of metals in and around star-forming
galaxies at . We combine empirically derived star formation histories
with updated supernova and AGB yields and rates to estimate the total mass of
metals produced by galaxies with present-day stellar mass of
--. On the accounting side of the ledger, we
show that a surprisingly constant 20--25% mass fraction of produced metals
remain in galaxies' stars, interstellar gas and interstellar dust, with little
dependence of this fraction on the galaxy stellar mass (omitting those metals
immediately locked up in remnants). Thus, the bulk of metals are outside of
galaxies, produced in the progenitors of today's galaxies. The COS-Halos
survey is uniquely able to measure the mass of metals in the circumgalactic
medium (to impact parameters of kpc) of low-redshift
galaxies. Using these data, we map the distribution of CGM metals as traced by
both the highly ionized OVI ion and a suite of low-ionization species; combined
with constraints on circumgalactic dust and hotter X-ray emitting gas out to
similar impact parameters, we show that % of metals produced by
galaxies can be easily accounted for out to
150 kpc. With the current data, we cannot rule out a constant mass of metals
within this fixed physical radius. This census provides a crucial boundary
condition for the eventual fate of metals in galaxy evolution models.Comment: 19 pages, 12 figures, 2 tables. ApJ, in pres
Applications of Fracture Mechanics to Accelerated Testing of Plastic Encapsulated Microelectronics
No abstract availabl
A Pilot Search for Population III Supernova Candidates in the Spitzer/IRAC Dark Field
We have undertaken a systematic search for candidate supernovae from
high-redshift Population III stars in a field that has been observed with
repeated imaging on a cadence of 2-3 weeks over a 2.2 year baseline, the
Spitzer/IRAC Dark Field. The individual epochs reach a typical 5-sigma depth of
1 uJy in IRAC Channel 1 (3.6 um). Requiring a minimum of four epochs coverage,
the total effective area searched is 214 sq arcminutes. The unprecedented depth
and multi-epochal nature of these data make it ideal for a first foray to
detect transient objects which may be candidate luminous Pair Instability
Supernovae from the primordial-metallicity first stars. The search was
conducted over a broad range of timescales, allowing for different durations of
the putative candidates' light curve plateau phases. All candidates were vetted
by inspection of the Spitzer imaging data, as well as deep HST/ACS F814W
imaging available over the full field. While many resolved-source objects were
found with Spitzer variability, no transient objects could plausibly be
identified as high-redshift supernovae candidates. The resulting 95% confidence
level upper limit is 23/sq deg/yr, for sources with plateau timescales under
400/(1+z) days and brightnesses above ~1 uJy.Comment: ApJL, in pres